Underdetermination Skepticism and Skeptical-Dogmatism
Abstract
The Mundane World Hypothesis (MWH) says that we have material bodies, we have brains
located inside our bodies, we have sense organs which process visual information, the direct cause of our
perceptual judgments is typically macroscopic material objects, and we live in a material world. Skeptics
using underdetermination arguments argue MWH has no more epistemic merit than some skeptical
competitor, e.g., that we are in the Matrix. Such competitor hypotheses are equipollent so, we are not
justified in believing MWH. This paper takes the underdetermination skeptic’s premises to a more radical
conclusion: skeptical-dogmatism, which is the view that MWH is probably false based on the idea that
there are many equipollent competitors to MWH.
1. Introductory
Underdetermination arguments for skepticism about the external world turn on the claim that
evidence for belief in the external world hypothesis is no better than some skeptical competitor
hypothesis, e.g., the hypothesis we are trapped in a virtual reality like the Matrix. Since evidence does not
favor the one hypothesis over the other, we have good reason to believe that we are not justified in
believing in the external world.1 The historical antagonists are dogmatists who claim we have justified
belief in the external world hypothesis. The main aim of the paper is to show that the usual
underdetermination considerations advanced in favor of skepticism about the external world actually
support a stronger conclusion, namely: we are justified in disbelieving the external world hypothesis,
since it is probably false.2 We will call this position ‘skeptical-dogmatism’.3 It sides with the dogmatist in
1
As should be evident, the skepticism at issue is not global because it still permits justified belief, although not
justified belief in the nature of the external world. See the final section where the distinction between ‘domestic’ and
‘exotic’ skepticism is discussed.
2
I take it that the reason to believe that the external world hypothesis is probably false provides good reason to
disbelieve it. However, I don’t take this to be a matter of strict entailment. It is a matter of a “Moorean-type” of
inference. After all, to deny the inference opens up one to the criticism of being saddled with a Moorean-type
absurdity: my philosophical position says ‘p’ is probably false but I don’t disbelieve ‘p’, where ‘p’ refers to the
external world. For more on these quasi-Moorean type paradoxes see Hájek (2007).
1
saying that a suspension of judgment is not warranted, and it sides with the skeptic in saying that a
positive verdict about knowledge or rational belief in the external world is not warranted.
A subsidiary aim is to show that skeptical-dogmatism provides its own unique challenges to
dogmatism. In part, this is because at least one of the premises supporting skeptical-dogmatism is weaker
than the corresponding premise in typical underdetermination arguments for skepticism. Furthermore, the
stronger conclusion of skeptical-dogmatism also means that at least some (unmodified) dogmatic
responses to underdetermination skepticism, including many forms of externalism, will not work against
dogmatic-skepticism.
2. A Tale of Two Professors and One Student
This section will illustrate the general contours of the argument with a tall tale. Subsequent
sections will develop and defend various parts of the informal version of the argument.
Imagine Illustrious University offers two sections of epistemology. Fickle, a philosophy major,
signs up for both sections with the aim of dropping one course and taking the section with the better
professor (meaning the professor with fewer course requirements). In Professor Relic’s class, Fickle
learns about underdetermination arguments for skepticism and their venerable history dating back to the
Ancient Greeks. Relic, blissfully unaware of his soporific powers, quotes Sextus Empericus to the class:
The Skeptic Way is a disposition to oppose phenomena and noumena to one another in
any way whatever, the result that, owing to the equipollence among the things and the
statements thus opposed, we are brought first to epochè and then to ataraxia. …At this
point we are taking as phenomena the objects of sense perception, thus contrasting them
with the noumena…By “equipollence” we mean equality as regards credibility and the
lack of it, that is, that no one of the inconsistent statements takes precedence over any
3
It may be thought that this is analogous to the ancient battle between Academic and Pyrrhonian skeptics. However,
the Pyrrhonian would have sympathy with the definition of the skeptic above, as would an Academic skeptic: an
Academic skeptic would make the further claim that we know that we do not know MWH, not that we know (or
have justified belief) that it is false. Obviously, asserting that P is not known does not imply knowing that P is false.
2
other as being more credible. Epochè is a state of the intellect on account of which we
neither deny nor affirm anything. (Mates 1996, 8-10)
Professor Relic points out that the idiom of ‘equipollence’ is somewhat antiquated, but the underlying
idea that we should suspend judgment when a belief lacks greater probability than some competitor is
familiar enough. A typical example is this: The police know the criminal worked alone (A. H. Goldman
2007). They have amassed evidence that equally supports the hypothesis that Bill committed the crime,
and the hypothesis that Phil committed the crime. The temptation to say that we ought to suspend
judgment about the innocence or guilt of Bill and Phil is clear. The Pyrrhonians thought such suspension
would induce a state of “quietude” (ataraxia).
Professor Relic asks the class to apply underdetermination thinking to whether our belief in the
external world is justified. He is quick to point out that the expression ‘the external world’ is a bit
unfortunate as it might seem to suggest that to overcome skepticism about the external world one need
only demonstrate justified belief in something external to one’s self. On this understanding, it seems that
a world with just you and Descartes’ evil demon will count as one where there is an external world.
However, ‘the external world’ is often thought to refer to something more specific like the Mundane
World Hypothesis (MWH). MWH holds, among other things, that (i) we have material bodies, (ii) we
have brains located inside our bodies, and (iii) we have sense organs that process visual information.
Furthermore, (iv) the direct cause of our perceptual judgments is typically macroscopic material objects
and (v) we live in a material world. In addition, (vi) our epistemic relationship to the world is
autonomous: evil demons, advanced aliens and so on, do not get involved in our epistemic lives.
Professor Relic points out that MWH is rather unremarkable: common sense, science and naturalized
epistemology agree in the main about MWH.4
I say “in the main” because there is room for disagreement about the details, e.g., naturalized epistemology tells us
that the brain “makes up” or fills in the details about the “hole” in our visual field which results from where the optic
nerve attaches to our eyeballs, whereas common sense epistemology is not aware of any such hole. A more serious
disagreement is about the status of the soul hypothesis, i.e., the dualism versus materialism debate. I take it that what
4
3
Professor Relic notes effects can often have many different causes. A house fire can be started by
an electrical fault, grease spilling on a stove burner, smoking in bed, arson, etc. Similarly, there are many
possible causes for our sensory experience. He asks the class to consider Berkeley’s competitor
hypothesis. Berkeley agrees that we directly see macroscopic objects, tables, trees, teacups, etc., but adds
that we perceive only ideas, so macroscopic objects are ideas (Winkler 1989, 138). When asked what
evidence might be offered in favor of the MWH over Berkeley’s World Hypothesis (SH2) the class
(under a bit of dialectical pressure) is quickly stymied. Relic points out that any such evidence would
have to be either a priori or empirical. He argues:
(i)
We have no a priori access about the nature of the causes of our experiences
which favors MWH.
(ii)
We have no empirical access to the nature of the causes of our sensory
experiences that favor MWH, since subjectively, our experience would be
indistinguishable if SH2 is true.5
Professor Relic, with triumphant glee, concludes that MWH is underdetermined: we are not justified in
believing MWH because it has no more going for it, evidentially speaking, than Berkeley’s hypothesis.
That is, since P(MWH/e) = P(SH2/e), where ‘e’ is the evidence available, we are not justified in believing
MWH.
Fickle hears almost the same lecture in his other epistemology class except Professor Nouveau
uses the hypothesis associated with the Matrix movie (SH1) instead of Berkeley’s hypothesis. (Professor
Nouveau hopes that the appeal to the Matrix movie is more interesting for his students and they will
reward him come student satisfaction survey time). Not surprisingly then, Professor Nouveau, with
triumphant glee, concludes that MWH is underdetermined: we are not justified in believing MWH
I have just described is consistent with what is usually thought about the soul hypothesis, e.g., that the brain is
responsible for processing some visual information. If one thinks that dualists and materialists ought not to be
lumped together like this, then the number of skeptical hypotheses that may be generated (see below) is greater than
without this assumption.
5
Clearly the professor is assuming some form of epistemic internalism. We shall follow suit. So, ‘evidence’ and
‘justification’ and their kin are understood in the usual internalistic manner.
4
because it has no more going for it, evidentially speaking, than the Matrix hypothesis. That is, since
P(MWH/e) = P(SH1/e), we are not justified in believing MWH.
Perhaps the most farfetched aspect of our story is that some university might offer two sections of
epistemology by two different professors in the same term. Other than that, I take it that the rest of the tall
tale is pretty standard stuff. The professors’ presentation of the underdetermination argument is familiar
enough. True, they differ in their choice of examples of competitor hypotheses, but this too is not
uncommon.6 I suspect the Matrix movie made it easy for some epistemologists to retire the brain-in-a-vat
hypothesis. Perhaps the movie Inception made it possible for some professors to retire the Matrix
hypothesis. Certainly it would make sense to discuss underdetermination with respect to either of these
movies in a philosophy of film class, while a professor teaching modern philosophy would have good
reason to follow Relic in using Berkeley’s hypothesis to illustrate underdetermination skepticism. In
short, I think it is quite plausible to assume that it is not uncommon to present underdetermination
arguments using different skeptical hypotheses to illustrate the argument.
Now for the rest of our tall tale: Fickle finds himself in the ironical position of finding equipollent
the question of which section of epistemology to drop. It seems both professors have assigned large
workloads and both seem equally incompetent. He decides to stick with the two classes for one more
week. The following week, Fickle points out to Professor Relic that Professor Nouveau argued in his
class that P(MWH/e) = P(SH1/e). Professor Relic agrees that this is correct. He could just as easily have
used the Matrix hypothesis to illustrate the point (but he has no need to fawn for high student evaluations
because he has tenure). Similarly, Fickle points out to Professor Nouveau that Professor Relic argued that
P(MWH/e) = P(SH2/e). Professor Nouveau agrees that this is correct. He could just as easily have used
Berkeley’s hypothesis (but then he would be a fuddy-duddy, like Professor Relic).
Fickle asks his professors about whether SH1 is identical with SH2. Both professors agree that
SH1 ≠ SH2. Indeed, they are competitors in just the same way that each is a competitor to MWH. Fickle
inquires further whether evidence favors SH1 over SH2 or vice versa. The professors agree that evidence
6
The idea that different skeptical hypotheses are often put up for consideration is endorsed by Pritchard (2012, 10).
5
does not favor the one over the other: there is no a priori reason to prefer one over the other, and
subjectively, one could not distinguish on the basis of sensory evidence, SH1 over SH2 or vice versa. So
the two professors agree that P(SH1/e) = P(SH2/e). But then there is an obvious problem in claiming that
we should neither affirm nor deny MWH. For if P(MWH/e) = P(SH1/e) and P(MWH/e) = P(PSH2/e) and
P(SH1/e) = P(SH2/e), then the maximum epistemic probability of MWH is 0.33. Indeed, transitivity and
the assumption that SH1 ≠ SH2 leads to the same conclusion. For if P(MWH/e) = P(SH1/e), and
P(MWH/e) = P(SH2/e), then P(MWH/e) = P(SH1/e) = P(SH2/e). In which case, again, the maximum
epistemic probability of MWH is 0.33. Fickle suggests that by the professors’ own premises it appears we
are in a position to say MWH is probably false. Fickle then asks each professor how this supports the
Pyrrhonian idea that we should “neither deny nor affirm anything,” since saying that MWH is probably
false is surely one way to deny MWH, and so epochè about the external world is thwarted. Fickle has
arrived at skeptical-dogmatism.
3. Ten Skeptical Hypotheses
In what follows, I shall try to spell out and defend the argument. Again, however, I shall not
attempt to defend the usual premises of the underdetermination argument, but rather, the dialectical
strategy will be to assume the usual premises of underdetermination arguments against knowledge of the
external world and see where they lead.7
One important idea that skeptical-dogmatism adds is that of multiple competitor hypotheses. This
difference is significant since underdetermination arguments are typically formulated in terms of a single
competitor.8 The minimum the argument for radical underdetermination of MWH requires is two
competitors. Clearly, however, there is any number of competitors to MWH. Here are a few, including
some of the most discussed:
7
See below for examples of what I take to be the usual premises of the underdetermination argument against
knowledge of the external world.
8
I don’t know of any formulations that have more than one competitor. Representative instances of single
competitor formulations include: Mates (1996); A. H. Goldman (2007); Hazlett (2006); Vogel (2005); and Pritchard
(2005a, 2012).
6
SH1: I am in the “Matrix”. I have a body. I live in a virtual reality constructed by an advanced
computer system that interfaces with my brain.
SH2: Berkeley was right that there are only minds and ideas; there is no material world.
SH3: I am in an “Inception” dream: a dream manipulated by others for the purposes of extracting
information.
SH4: I am a brain-in-a-vat. I lack a body. I live in a virtual reality controlled by an advanced
computer system that interfaces with my brain.
SH5: I am deceived by Descartes’ evil demon.
We can easily create more. And so, in deference to cultural skeptical diversity, let us suppose:
SH6: I am deceived by Anhaka (Hindi demon).
SH7: I am deceived by Bushyasta (Zoroastrianism demon).
Other skeptical possibilities include:
SH8: There is a material world, but we are brains-in-a-vat held in an underground laboratory by a
mad scientist. Our bodies are robots that walk the earth. Information is sent between the robots and our
brains in the underground laboratory via radio waves.
SH9: There is a material world, but we are brains-in-a-vat held in an underground laboratory by a
mad scientist. Our organic bodies are brainless zombies but nevertheless, they walk the earth. Information
is sent between our bodies and our envatted brains via radio waves.
SH10: We are purely electronic beings living in a computer simulation of the MWH.
MWH is incompatible with each of SH1-10. Indeed, we should understand all eleven hypotheses as
logical contraries: in any pairwise comparison, both may be false but both cannot be true.9
9
The skeptical hypotheses above need to be spelled-out in more detail to show that each is a contrary to the other
nine. For example, a possibility we will consider below is that the Matrix is part of an immaterial world. The virtual
world of the Matrix is powered by computers, which are ideas in Berkeley’s sense. This would suggest that SH1 and
SH2 are not contraries. To avoid this, we can stipulate at this stage that Berkeley’s hypothesis is committed to the
falsity of any virtual reality. Below we will show that at least some of the skeptical hypotheses are logical contraries.
7
Not only have a number of competitors to MWH been discussed in the literature, but the fact that
MWH makes a number of claims about reality (described by Relic in (i) to (vi) above) gives us good
reason to think that MWH has multiple competitors. After all, denying one conjunct of (i) to (vi) is
sufficient to deny MWH, so this fact alone opens up the possibility of multiple competitors to MWH. We
shall return to this point below in more detail.
4. Underdetermination and Radical Underdetermination Principles
As noted, underdetermination principles are typically formulated in terms of a single competitor.
A characteristic formulation is provided by Hazlett:
U2: Underdetermination Justificatory Principle (UJP): “If h1 and h2 are hypotheses and
e is all S’s evidence, S is justified in believing h1 only if P(h1/e) > P(h2/e) (2006, 200).”
It will be convenient to use Hazlett’s formulation in what follows, but it is worth saying something about
different formulations of the underdetermination principle. The following comes from Jonathan Vogel:
UP1: “If q is a competitor to p, then a subject S can know p only if p has more epistemic
merit (for S) than q (2005, 73).”
Duncan Pritchard offers:
UP2: “For all S, p, q, if S’s evidence for believing p does not favour p over some
hypothesis q which S knows to be incompatible with p, then S’s evidence does not justify
S in believing in p (2005b, 39).”10
To say that q is a competitor or incompatible with p is typically understood, as noted above, as implying
that they are logical contraries: if q is true, then p is false. What is the relation between these two? UP1
seems weaker as it does not rule out the possibility that S may have a justified belief in p, only that the
justification is insufficient for knowledge. Conversely, UP2 implies that p is not known when evidence
does not favor it (on the assumption that justification is necessary for knowledge). For ease of exposition
I assume the interested reader can imagine further dressing up the skeptical hypotheses to ensure that they are all
logical contraries.
10
For a nearly identical formulation see Brueckner (1994)
8
we will focus on UP2: nothing of substance hangs on the potential gap between justified belief and
knowledge in the present context.11
At first blush, the connection between epistemic merit mentioned in Vogel’s formulation and
favoring in Pritchard’s formulation, and the underdetermination skeptic’s claim that our belief in the
MWH is not justified, may seem puzzling. After all, it seems that sometimes epistemic merit or favoring
may have little to do with justification or truth. A model showing the sun as the center of the solar system
may have the epistemic merit of (or have in its favor) increased student understanding, but strictly
speaking, it is false according to our best physics. To avoid such worries it will be helpful to directly
connect the notions of ‘epistemic merit’ and ‘favoring’ in terms of epistemic probabilities. One
connection can be made via the translation principle. Let ‘e’ be the total sensory and non-sensory
evidence available to some subject S:
Translation Principle: If h1 has more epistemic merit than h2 for S, or S’s evidence (e)
favors h1 over h2, then P(h1/e) > P(h2/e) for S.
The translation principle allows us to go from UP2 to U2, which, as noted, we will employ in subsequent
discussion.
To allow for multiple competitors, think of ‘radical underdetermination’ as the situation where
there are two or more competitor beliefs or hypotheses and think of ‘run-of-the-mill underdetermination’
(hereafter just ‘underdetermination’) as having a single competitor to some belief or hypothesis.12 We
will define radical underdetermination in terms of two competitors, but this is a minimum which we will
use simply for illustrative purposes. The number of competitors can be multiplied without limit.
11
It should be clear that UP1 and UP2 are formulated on internalist lines where there is a tight connection between
justification and having evidence (or perhaps access to evidence) that justifies the belief. Various forms of
externalism and entitlement theories challenge this assumption. I do not defend it here because it is an assumption of
the underdetermination arguments we will canvas. The difference between underdetermination and radical
underdetermination arguments vis-à-vis externalism is canvased very briefly in the final section.
12
Thus this use of ‘radical skepticism’ is quite different from Sklar’s (1975).
9
RU2: Radical Underdetermination Justificatory Principle (RUJP): If h2 and h3 are
competitor hypotheses to h1, and e is all S’s evidence, S is justified in believing h1 only
if P(h1/e) > P(h2/e) and P(h1/e) > P(h3/e).
Articulating RUJP in terms of the legal illustration, the belief that Bill is guilty is not justified if the
evidence equally points to two other suspects, Phil and Dill. It is clear that RUJP is weaker than UJP.
Other things being equal, the justification for believing that Bill is guilty when there is only one other
suspect is greater than the justification for believing that Bill is guilty when there are two other suspects
equally incriminated by the evidence. So, if one thinks that UJP provides a necessary condition for
justified belief, as obviously the underdetermination skeptic must, then one should think the same of
RUJP.
It is worth noting the maximum epistemic probability permitted by RUJP. If H1 does not have
more epistemic merit than either of its competitors H2 and H3, then the maximum probability of H1 is
one third of the total probability, that is, (approximately) 0.33.13 For suppose H1 had a higher probability,
say 0.5, as in the underdetermination illustration above. This would mean that the other two competitors
would have only 0.5 epistemic probability to divide amongst themselves, and so the two competitors
would then have an average probability of only 0.25, in which case we would have good reason to
suppose that H1 is not radically underdetermined.
5. Underdetermination Vs. Radical Underdetermination Arguments
Underdetermination arguments for external world skepticism are typically expounded as
comprising a major and minor premise.
U1: S’s evidence for believing MWH is not greater than S’s evidence for
believing SH2.
By ‘approximate’ I mean within 0.01. Here and below we shall ignore these small probabilities for ease of
exposition. Further niceties are to be understood as implicit, e.g., we are assuming that the epistemic probabilities
are assigned by a sufficiently rational agent who understands that the hypotheses are mutually incompatible, and
who correctly utilizes this information when assigning epistemic probabilities.
13
10
U2: Underdetermination Justificatory Principle (UJP): “If h1 and h2 are
hypotheses and e is all S’s evidence, S is justified in believing h1 only if P(h1/e) >
P(h2/e) (Hazlett 2006, 200).”
UC1: S is not justified in believing MWH.
Very similar formulations to this are made by a number of authors including Vogel (1990, 2005),
Pritchard (2005a) and Hazlett (2006).
Interestingly, the usual presentation of underdetermination arguments in the literature shows how
skepticism about MWH is motivated, but they fall short of demonstrating the equipollence of MWH and
SH2. Indeed, it might be wondered whether the dogmatist might find this line of argument congenial, or
at least not devastating, if true. For suppose we are trying to decide between two competitor hypotheses,
and we are told that one is not justified, this leaves open the possibility that the other is justified. Consider
the analogous situation in science. Suppose there are two competitor hypotheses: Newtonianism versus
Einsteinianism. A scientist who believes in Newtonianism is confronted with an argument that
Newtonianism is not justified. A little disconcerted, the scientist nevertheless takes solace in the fact that
this lends support, or at least does not prohibit, justified belief in Einsteinianism. Analogously, the
dogmatist might hold out hope that the above argument does not prohibit justified belief in SH2. A
Berkeleyian dogmatist, someone (like Berkeley himself) who thinks that SH2 is justified, could welcome
the underdetermination argument against MWH.
However, the underdetermination skeptic will also challenge the thought that SH2 might be
justified:
U3: S’s evidence for believing SH2 is not greater than S’s evidence for believing
MWH.
U3 combined with U2 provides all that is needed to conclude that SH2 is also not justified. To arrive at
the idea that MWH and SH2 are equipollent, it seems the underdetermination skeptic must invoke
something like the following:
11
U4: Underdetermination Alethic Principle: If h1 and h2 are competitor
hypotheses, and S’s evidence for believing h1 is not greater than S’s evidence for
believing h2, and S’s evidence for believing h2 is not greater than S’s evidence for
believing h1, then h1 and h2 are equipollent: “equality as regards credibility and the lack
of it, that is, that no one of the inconsistent statements takes precedence over any other as
being more credible.”
So, U4 combined with U1 and U3 entitle the skeptic to conclude:
UC2: MWH and SH2 are equipollent.
U1 and U2 need little discussion in this context. As mentioned more than once, the dialectical
strategy is to accept the usual reasons offered in support of underdetermination arguments for skepticism
and see where they lead. I have pointed out that U3 and U4 are necessary for the underdetermination
skeptic to show equipollence and to ensure that the usual underdetermination argument (U1, U2 and UC)
are not used in support of an argument to the effect that we have reason to deny MWH.14 UC2 is
understood as the idea that there is no evidence favoring MWH over SH2 and no evidence favoring SH2
over MWH. Alternatively, we can say that MWH and SH2 are equally epistemically probable: neither has
a greater epistemic probability than the other.
The first part of the radical underdetermination argument is structurally similar to what I
described above as the usual presentation of underdetermination arguments:
RU1: S’s evidence for believing MWH is not greater than S’s evidence for
believing SH1, and S’s evidence for believing MHW is not greater than S’s evidence for
believing SH2.
RU2: Radical Underdetermination Justificatory Principle (RUJP): If h2 and h3
are competitor hypotheses to h1, and e is all S’s evidence, S is justified in believing h1
only if P(h1/e) > P(h2/e) and P(h1/e) > P(h3/e).
14
The point is familiar enough from the Pyrrhonian tradition: to undermine dogmatic belief, Pyrrhonians need to be
very careful to not overshoot and make a stronger argument in favor of not-p. See Sorrenson (2004, 229-231).
12
RUC1: S is not justified in believing MWH.
RU1 says that MWH has no epistemic advantage over SH1 and SH2. This seems to be assumed
in the usual presentation of underdetermination arguments as evidenced by the teachings of Professors
Relic and Nouveau. We noted above that RUJP is weaker than UP. This is confirmed when we realize
that RUJP is compatible with the claim that MWH is justified when its epistemic probability is as low as
0.34 where the epistemic probability of SH1 and SH2 are each 0.33. UP, on the other hand, requires at
least a 0.51 epistemic probability, and so is a more stringent requirement. RUC1 follows from modus
tollens on RU1 and RU2.
The remainder of the radical underdetermination argument is as follows:
RU3: Radical Underdetermination Alethic Principle (RUAP): If h2 and h3 are
competitor hypotheses to h1 and to each other, and e is all S’s evidence; and S’s evidence
for believing h1 is not greater than S’s evidence for believing h2, and S’s evidence for
believing h1 is not greater than S’s evidence for believing h3, then h1 is probably false.
RUC2: MWH is probably false.
RUC3: Some competitor hypothesis to MWH is probably true.
The reasoning for RU3 is that it is entailed by U4. Recall, we are understanding equipollence in
terms of equal credence or epistemic probability. As Fickle argues above, a consequence of this
assumption is that the maximum epistemic probability of MWH is 0.33, when the epistemic probability of
MWH equals that of SH1, and the epistemic probability of MWH equals that of SH2, where SH1 ≠
SH2.15 Modus tollens on RU1 and RU3 allows us to arrive at RUC2, that is, skeptical-dogmatism. RUC3
follows from RUC2: it is more likely that some competitor of MWH is true. Of course, the same can be
said of each of the competitors: the radical underdetermination argument says for any particular
15
It should be clear, then, that the radical underdetermination argument for dogmatic-skepticism which assigns 0.33
probability in the example under consideration does not depend on an appeal to a principle of indifference ((Keynes
2004)) Rather, this is simply a consequence of the underdetermination skeptic’s claim of equipollence of three
logical contrary hypotheses. Indeed, we can get to the dogmatic-skeptical conclusion simply by supposing that two
hypotheses are equipollent and there is some third logically incompatible hypothesis with some non-zero
probability. See note 19 for elaboration of the point.
13
hypothesis that it is probably false and some competitor true. The reason for focusing on MWH in RUC2
and RUC3 is simply that MWH is near and dear to many.
This completes the preliminary defense of the argument. I will expand and defend the argument
further below through the consideration of a number of objections.
6. Objection: There is only one skeptical hypothesis
Much of the weight of the argument turns on RU1. In most general terms, it is relatively
straightforward to see why this is the case. As noted, both the underdetermination skeptic and the
skeptical-dogmatist accept that MWH is at least underdetermined. From this it follows that the maximum
epistemic probability of MWH is 0.5. The residual disagreement is about radical underdetermination:
whether the epistemic probability of MWH is actually lower than 0.5. We will examine maneuvers for the
underdetermination skeptic to avoid the skeptical-dogmatist’s claim that the epistemic probability of
MWH is lower than 0.5. One line of objection, which we will consider in this section, is the idea that
there are fewer skeptical hypotheses than advertised in the radical underdetermination argument; a second
line of objection, discussed in the following section, is the idea that there are more mundane world
hypotheses than advertised.
We can initially formulate the first line of objection by the underdetermination skeptic thus: there
are really only two significant hypotheses at play: MWH and ¬MWH, and so there is only one significant
skeptical hypothesis: ¬MWH. The various skeptical hypotheses listed above (SH1 to SH10) are merely
different ways of illustrating ¬MWH. If this line of objection is correct, the skeptic may maintain that
MWH is underdetermined because of its equipollence with ¬MWH, but MWH is not radically
underdetermined.
However, to say that the various skeptical hypotheses are simply different ways of saying
¬MWH, the skeptic cannot be thinking that the set of skeptical hypotheses are logically equivalent or
merely notational variants. As noted above, the skeptical hypotheses are intended to be logically
independent in the sense that if one is true, then the other nine are false. For example, if SH4 is true, then
14
people are armless (and, indeed, bodiless) brains-in-a-vat. If SH1 is true, people are not armless when
they are plugged into the Matrix.16
So, to say that the individual skeptical hypotheses merely illustrate ¬MWH does not really help.
The underdetermination skeptic must choose a horn: either the probability of ¬MWH is equal to the
probability of one skeptical hypothesis or to several skeptical hypotheses. If the probability of ¬MWH is
equal to that of some particular hypothesis, then the remaining hypotheses must be assigned a probability
of zero. To say that we are in a position to be certain that every skeptical hypothesis but one is false
seems an untoward consequence for the underdetermination skeptic. After all, even some (perhaps most)
dogmatists may be willing to grant that there is some tiny probability that we are in the Matrix or that
Berkeley was right.
More plausibly, the underdetermination skeptic might want to say something along the following
lines: the probability of ¬MWH is simply the conjunction of the individual probabilities of the ten
skeptical hypotheses. (Let us grant for the moment that there are only ten skeptical hypotheses). Let us
assume further that they are evidentially equal, the probability of any individual skeptical hypothesis is
0.0517.
The obvious question to ask here is what reason the underdetermination skeptic has for thinking
that the probability of MWH equals the set of skeptical hypotheses (the ‘skeptical set’ for short).18 The
question, in other words, is why should we believe the probability assignments suggested by the
underdetermination skeptic as opposed to the dogmatic-skeptic? To argue, given the underdetermination
skeptic is correct, then the probability that MWH is true must be equal to the probability of the skeptical
set, is clearly not going to work. For this would be to argue from underdetermination skepticism, not to
underdetermination skepticism. In other words, to simply assume this is the correct probability
assignment is to beg the question.
16
As noted above, the hypotheses will need to be spelled out in more detail to ensure that they are logical contraries.
See note 19 for the innocuousness of this assumption
18
So, U1 of the underdetermination argument will have to be reformulated to allow comparison between individual
hypotheses and sets of hypotheses.
17
15
Perhaps the underdetermination skeptic will think to appeal to the “negation argument”: The fact
that we can use negation to draw two categories shows that each category is equally probable. A die
might be divided into two categories: “sides with the number ‘1’”, and “sides without the number ‘1’”.
On this understanding, the sides marked ‘2’, ‘3’, ‘4’, ‘5’ and ‘6’ are simply ways of illustrating not-sides
with the number ‘1’, but clearly it would be wrong to conclude that the probability of the die landing on 1
is the same as it landing on not-1. This does not show that the underdetermination skeptic is wrong in
assigning a 0.5 probability to the skeptical set, but it does show that the reasoning for this assignment
cannot be that the negation argument works in all instances.
We will look at three arguments, which we will term ‘undermining’, ‘symmetry’ and
‘specificity’, that show that the underdetermination skeptic cannot reasonably hope to assign a 0.5
probability to the skeptical set.
6.1 The Undermining Argument
The undermining argument turns on the insight that dividing the 0.5 probability amongst the
skeptical competitors undermines the original impetus behind the underdetermination argument. If the 0.5
probability is divided equally amongst the skeptical set, Professors Relic and Nouveau must be wrong
about their versions of the underdetermination argument. For, as we noted, Professor Nouveau says that
MWH and SH1 are equipollent and Professor Relic says that MWH and SH2 are equipollent. On the
revised understanding, MWH is ten times more likely: a 0.5 probability for MWH and merely a 0.05
probability for each of SH1 and SH2. If so, then it would seem the students have good grounds to
(logically) beat their professors: they can say SH1 and SH2 are not evidentially equal to MWH.
Furthermore, students can pose a very embarrassing question: What evidence can the professors
offer for favoring MWH over SH1 and SH2? If MWH is not underdetermined with respect to SH1 and
SH2 individually, then it must be that either sensory evidence or a priori evidence favors MWH in
pairwise comparisons. There is nothing to suggest that the underdetermination skeptic should now think
that sensory evidence favors MWH. The only a priori reason for favoring MWH seems to be the idea that
the 0.5 probability must be divided up amongst the skeptical set in order to save the underdetermination
16
skeptic. But again, this is to argue from rather than to the conclusion that the probability of the skeptical
set is 0.5.
It might help to think about what would work, at least in principle. A non-question begging a
priori argument for assigning 0.5 to the skeptical set might be something like one of the following: We
have an a priori proof that God exists and he is a nice guy who probably wouldn’t want us deceived, so
there is only a 0.05 probability that he would permit SH1 and a 0.05 probability of SH2 and so on.
Likewise, transcendental arguments concerning the possibility of language interpretation or meaning
might be invoked to show that the skeptical set ought to be assigned a 0.5 probability. These suggestions
are, of course, probabilistic versions of Descartes (1993), Davidson (2006) and Putnam’s (1981) a priori
arguments against skepticism. Since nothing like this is offered, we must conclude that the
underdetermination skeptic’s assignment of probabilities associated with the skeptical set is merely to
avoid radical underdetermination. And the underdetermination skeptic cannot simply allow probabilities
to be assigned on the basis of one’s preferred epistemological position, for then the underdetermination
skeptic is hardly in a position to complain if the dogmatist assigns a higher probability to MWH in order
to avoid underdetermination skepticism.
An analogy will help amplify this argument. Suppose an underdetermination skeptic and a
dogmatic-skeptic, weary of arguing, decide to clean the attic, where they find an old-style Christmas light
string in a box. It appears that the light string has not been touched in at least ten years. They wonder
whether the light string will work: it is wired in series so all six lights must be in working order for any
bulb on the string to light. They confer and neither has any information about the reliability of Christmas
lights. They speculate that perhaps such bulbs have 100% reliability for a thousand years, perhaps they
have 95% failure rate each passing month when not in use. Agreeing that they have no knowledge of the
reliability of the bulbs, they decide it is equipollent whether any particular bulb is in working order. The
underdetermination skeptic adds that the hypothesis that the string will work when plugged in is
equipollent with the hypothesis that the string won’t work.
17
The dogmatic-skeptic charges the underdetermination skeptic with an inconsistency. For on the
one hand, if there is a 0.5 probability that each bulb will work, then the probability of the entire string
working is 0.015625 (that is, the product of the individual probabilities of each light working). But then,
the truth of the proposition that the Christmas string will light is radically underdetermined, contra the
underdetermination skeptic. On the other hand, if the probability of the string working or not is
equipollent, as the underdetermination skeptic maintains, then the average probability of each bulb
working must be about 0.9. So, the claim of equipollence of the string working or not commits the
underdetermination skeptic to a high degree of confidence that each bulb will work. The
underdetermination skeptic can’t have it both ways: either it is equipollent that each bulb is in working
order, or it is equipollent whether the entire string will light.
Similar things should be said about the underdetermination skeptic’s attempt to say that whether
MWH is true or false is equipollent. For MWH has critical subcomponents, also, if any one of (i) to (vi) is
false, then MWH is false. So the same dilemma must be faced. If the truth or falsity of MWH is
equipollent, then the average probability of each of the six subcomponents of MWH must be about 0.9.
But this conflicts with the underdetermination skeptic’s claim that very general features about our
epistemic situation lie beyond our ken. While it may not be a problem for dogmatists, surely it would be
of some embarrassment to underdetermination skeptics to claim that they are 0.9 confident on average for
each of the claims we have attributed to MWH: (i) we have material bodies, (ii) we have brains located
inside our bodies, (iii) we have sense organs which process visual information, (iv) the direct cause of our
perceptual judgments is typically macroscopic material objects, and (v) we live in a material world. In
addition, (vi) our epistemic relationship to the world is autonomous: evil demons, advanced aliens and so
on, do not get involved in our epistemic lives. But only this high level of average confidence is consistent
with the claim that MWH is underdetermined. On the other hand, if the underdetermination skeptic
concedes that the truth or falsity of the critical subcomponents of MWH is equipollent, the argument is
lost, for then MWH is radically underdetermined.
18
The analogy also helps us diagnose the underdetermination skeptic’s error. The adoption of
radical underdetermination of the Christmas light string is motivated in part by a crucial bit of knowledge,
namely, the realization that the string will work only if every light is in working order. A similar point
applies to the MWH: both the skeptic and dogmatic-skeptic accept that MWH is true only if all of (i) to
(vi) are true. So, both the Christmas light string and MWH have critical “parts”: They must be in working
order, or true, for the whole to be in working order, or true. But, as we have seen, if we accept
equipollence about each of the parts, then the whole must be radically underdetermined. If we accept that
the whole is underdetermined, then we are committed to a high degree of confidence about the working
order or of the truth of the parts. Either horn undermines the impetus behind the original
underdetermination argument.19
6.2 The Symmetry Argument
Another line of objection is that MWH is evidentially different because the other hypotheses are
“mere skeptical hypotheses”, simply different ways of saying not-MWH. However, in thinking that MWH
is special amongst all the possible hypotheses about the nature of reality, e.g., in thinking that it takes the
entire skeptical set to be equipollent with MWH, underdetermination skeptics have not sufficiently purged
themselves of the lingering effects of dogmatism. At least, this is what the symmetry argument maintains.
It will be best to illustrate with a little story before spelling out the argument.
As far as they could tell, Relic’s students were the only survivors of the great nuclear holocaust of
2013. They established their tribe on the belief that Berkeley is right: reality is ultimately just minds and
ideas. Professor Relic’s last words before the bombs hit were in defense of the equipollence of Berkeley’s
hypothesis with MWH. Students took Professor Relic’s defense to be in support of Berkeley’s view over
19
It should be clear too that nothing in the argument depends of the indifference principle, in particular, on dividing
the epistemic probability equally amongst the skeptical set. Suppose, for example, professors Relic and Nouveau put
their heads together and agree that SH2 is far more likely than SH1, but SH2 still has a tiny bit of epistemic
probability. There is still a problem for the underdetermination skeptic. For if on this revised assessment MWH and
SH2 are equipollent, and SH2 has some small epistemic probability, then the probability of SH1 and SH2 is greater
than that of MWH, which undermines the underdetermination argument. Likewise, there is still a problem for the
underdetermination skeptic in showing that the probability of the skeptic set equals exactly 0.5 even when the
skeptical hypotheses are not accorded equal credence.
19
MWH. (This atrocious misunderstanding of Professor Relic’s lecture may be due to the fact that most of
them were texting during his class. The rest were asleep). His students, never shy of a post hoc fallacy or
two, took it as a sign from God that Berkeley was right; and to escape further reprisals, they ought to
believe in Berkeley’s view. Within a few generations, the original reasons for believing the Berkeleyian
world view were forgotten. The tribe continued to believe in Berkeley’s view simply because this was the
metaphysics they learned on their mothers’ knees.
After several hundred more years, a miraculous discovery was made: a tribe member stumbled
across a working DVD player from 2013. The hunter gatherers had, of course, heard stories about the
wondrous technology of the ancients, but here was the first chance to see it with their own eyes.
Unfortunately, the only DVD was the one in the player: The Matrix. After watching the film, a few of the
hunter gatherers became convinced that they were in the Matrix. This offered an intuitively satisfying
explanation for the devastation of the ancient civilization. Of course, this new metaphysical view
conflicted with the received view. Unable to reconcile their metaphysical differences, the tribe split into
two: the Berkeleyians and the Matrixians. Both believed that reality is ultimately ideas and minds, but the
Matrixians believed that machines had enslaved them in a virtual reality run by a computer (where the
computer is ultimately an idea).
This, in any event, was the official position of each tribe. There were a few members of both
tribes who quietly discussed the possibility that each tribe’s beliefs were equipollent and that the right
thing to do would be to suspend judgment as to whether the Berkeleyians or the Matrixians were right.
But, of course, skeptics are never popular.
It turns out there was a third group of survivors, the Mundanes, who believed MWH. One day, a
scout from each of the three tribes met by chance. Over a meal of roasted giant, post-apocalyptic
cockroaches, the Berkeleyians and Matrixians were aghast to hear about the primitive metaphysics of the
mundane world hypothesis. According to the Berkeleyians and the Matrixians, it was only common sense
that reality is ultimately ideas. The only serious question for dispute was whether they were part of a
computer simulation in an immaterial world.
20
When the scouts reported back to their respective groups, it was resolved by the leaders of each
tribe that it would be in their mutual interest to work together to survive in the harsh environment, but
only so long as they could resolve their deep metaphysical differences. A philosophical convention was
convened to sort out their disagreements. Dogmatists and underdetermination skeptics from each group
were invited to speak.
A dogmatist from each group argued that it is right to take “intuitive appearances at face value,”
(Pryor 2000, 536) but they disagreed about what intuitive appearances reveal. The dogmatists amongst the
Mundanes believed that it reveals the truth of MWH; the dogmatists amongst the Matrixians believed that
intuitive appearances reveal the truth of SH1; and the dogmatists amongst the Berkeleyians believed that
intuitive appearances reveal the truth of SH2. Other dogmatists offered inference to the best explanation
arguments: the Berkeleyians claimed their metaphysics was simpler than the Mundanes. Whereas the
Mundanes appealed to matter, ideas and minds, the Berkeleyians needed only to appeal to the latter two
(Fumerton, 1992, 2005). The Matrixians said that the Matrix view offered the only plausible explanation
as to how an advanced civilization like that of the Ancients could catastrophically collapse. They said it
was hard to believe that humans would be so stupid as to inflict such devastation on themselves—
machines must have had a hand in it. So, what it lacked in simplicity, the Matrixians claimed their
hypothesis made up for in terms of another value in theory adjudication: explanatory scope (Kuhn 1977).
Most interesting for our purposes is the argument from underdetermination skeptics from each
group applied. They claimed that the probability of their home field metaphysical hypothesis was equal to
the probability of it not being correct. So,
Matrixians: (P)SH1=(P) ¬SH1
Berkeleyians: (P)SH2=(P) ¬SH2
Mundanes: (P)MWH=(P) ¬MWH
The skeptical set for each group is the set of the hypotheses of their neighbors. But, the inconsistency here
is glaring (assuming the probabilities are not zero), since the negation of each home field hypothesis is
equivalent to the affirmation of the other two home field hypotheses. So we have the following:
21
(1) (P)SH1=(P)SH2 + (P)MWH
(2) (P)SH2=(P)SH1 + (P)MWH
(3) (P)MWH=(P)SH1 + (P)SH2
But then we can derive the following inconsistency by substitution:
(4) (P)SH2=[(P)SH2 +(P)MWH] + (P)MWH [from 1 and 2]
In other words, the problem is that the subjective credence assigned by each group to its home field
hypothesis is 0.5, for a combined total of 1.5. The only way to simultaneously satisfy (1)-(4) is if the
probability of each is 0.0, which is the strongest possible form of thinking that MWH is false.
The point here is not to assert that the skeptic has the upper hand in arguing with the dogmatist,
but to notice the reasoning the skeptic uses against the dogmatist: the underdetermination skeptic from
each tribe simply assumed that the negation of the home field hypothesis was 0.5 without any argument.
What is missing is a very delicate argument that some home field hypothesis has more epistemic merit
than each of its competitors, but not so much epistemic merit that is has more than the combined
epistemic merit of the set of competitor hypotheses. The missing argument must be “delicate” because too
much epistemic merit for the home field hypothesis will have the underdetermination skeptic sliding into
dogmatism, e.g., the argument that considerations of explanatory adequacy favor SH1 (A. H. Goldman
2007, Vogel 1990 and BonJour and Sosa 2003). If the underdetermination skeptic helps himself to
explanatory adequacy in order to show that SH1 has more epistemic merit than either MWH or SH2, and
this epistemic merit raises the probability of SH1 above 0.5, then this is the result desired by the
dogmatist. If the epistemic merit of explanatory adequacy does not reach 0.5, then this result will be
welcomed by the skeptical-dogmatist.
The symmetry argument also brings to the fore the fact that none of the hypotheses under
consideration is intrinsically a skeptical hypothesis compared with any other. Each of the hypotheses is a
metaphysical hypothesis in this sense: they offer an explanation of the character of our sensory experience
in terms of some of some general features of the world. The locution ‘skeptical hypothesis’ in this context
is simply a comparative term denoting a competitor to the received view: a society that believed in
22
Berkeley’s metaphysics would classify MWH as a skeptical hypothesis. The symmetry argument, then,
shows that there is nothing inherently skeptical about SH1-SH10 that serves to differentiate it from
MWH: where MWH is not the received view, it too is a skeptical hypothesis.
6.3 The Specificity Argument
The specificity argument turns on considerations about the relationship between less specific and
more specific statements about some subject matter. There is a general correlation between the specificity
of some hypothesis about some given subject matter and the number of logically incompatible
hypotheses: typically the more specific a hypothesis is about some given matter, the greater the number of
logically incompatible hypotheses; and the less specific a hypothesis about some given subject matter, the
fewer the logically incompatible hypotheses (other things being equal). Detective Clouseau announces a
very specific hypothesis: the victim was killed in the drawing room with a candlestick by Colonel
Mustard. Detective Piorot thinks such a proclamation rash given the paucity of evidence. Piorot commits
only to the vaguer hypothesis that the murderer was a male. There are any number of hypotheses that are
inconsistent with Clouseau’s hypothesis that are not inconsistent with Piorot’s. For example, the murderer
was Colonel Mustard but he used a hammer rather than a candlestick to kill the victim. Conversely, any
hypothesis that is inconsistent with Detective Piorot’s hypothesis is also inconsistent with Clouseau’s
hypothesis. In what follows, we will stipulate that the more specific/less specific relationship of concern
has this relationship: a more specific hypothesis about some given subject matter implies the less specific
hypothesis, but not vice versa.20
With this understanding, we can see that the more specific a hypothesis, the more evidence will
be required for justification. Any body of evidence that justifies the more specific hypothesis will justify
the less specific hypothesis, but not vice versa. Corollaries of this observation are, with one small proviso
to be mentioned in a moment, (a) if a less specific hypothesis is underdetermined, then the more specific
20
It is a stipulation since not all more specific/less specific contrasts will have this relationship. To say the killer is
143cm tall, walks with a limp, reads Tolstoy and lived in southern France as a child is more specific than saying the
killer is a male. But the former is compatible with the killer being either male or female.
23
hypothesis is radically underdetermined; and (b) if the more specific hypothesis is underdetermined, then
the less specific hypothesis is not underdetermined.
To understand the proviso we need to think a bit more about the relationship between the less
specific and more specific hypotheses as we have defined them. We may stipulate this formula:
The meaning of a more precise hypothesis = the meaning of the less specific hypothesis
plus the surplus meaning.
The ‘surplus meaning’ is simply what the more specific hypothesis says above and beyond the less
specific hypothesis. The definitions are inherently circular, but this is not a problem for present purposes
for they are only intended to give us a convenient vocabulary. To see these distinctions in action, think
again about Cousteau and Piorot. Part of what they mean by their respective hypotheses overlaps: the
murderer is male. The surplus meaning of Cousteau’s hypothesis is what it says beyond this overlap,
namely, that the male in question is Colonel Mustard who used a candlestick in the drawing room.
We can see why, in general, we would suspect that if the less specific hypothesis is
underdetermined, then the more specific hypothesis is radically underdetermined. For suppose Piorot’s
hypothesis is underdetermined. This means that we should assign no more than a 0.5 probability that the
murderer is a male. The probability that Cousteau is correct is, at most, 0.5 because a necessary condition
for his hypothesis being true is that the murderer is a male. However, the only way that the probability
could be as high as 0.5 is if Cousteau were in a position to be certain about the truth of the proposition
expressed by the surplus meaning. For example, if Cousteau is certain of this conditional: if the murderer
is a male, then the murder was perpetrated by Colonel Mustard in the drawing room with a candlestick.
The reason certainty is required is that we must multiply the probabilities of the two components, the
overlapping meaning and the surplus meaning, to find the probability of the more specific hypothesis. So,
if the proposition expressed by the overlapping meaning is underdetermined, then the only way the more
precise hypothesis can be underdetermined is if the proposition that expresses the surplus meaning is
certain. Anything less than certainty and the more specific hypothesis will become radically
underdetermined. For example, suppose Cousteau is only 0.95 confident of the conditional: if the
24
murderer is male, then the murder was perpetrated by Colonel Mustard in the drawing room with a
candlestick. In which case, the probability that Cousteau is right drops to 0.475, the product of the two
probabilities. This would mean that Cousteau’s hypothesis is radically underdetermined: it is more likely
that the crime was committed either by a woman or not by Colonel Mustard with a candlestick in the
drawing room. Conversely, if Cousteau’s hypothesis is underdetermined, then Piorot’s is not
underdetermined, except in the rare (if ever) circumstance where the proposition associated with the
surplus meaning is certain. Suppose that Cousteau is only 0.95 confident of the aforementioned
conditional. This means that if Cousteau is 0.5 confident that he is correct, then the confidence that the
perpetrator is male must be 0.53. Of course, with this confidence level, Piorot’s hypothesis is not
underdetermined.
Consider that MWH is a fairly specific hypothesis. As we noted several times, it requires (i) to
(vi) above. Indeed, as intimated above, terming skepticism about MWH ‘external world skepticism’ is a
very misleading gloss. Each of SH1to SH10 is compatible with the claim that the external world exists.
To cite our earlier example, if the entire universe comprises just you and an evil demon, then the evil
demon is the entirety of the ‘external world’. I’m not suggesting that this ought to be offered as solace to
those worried about external world skepticism; rather, that ‘external world skepticism’ must often be
understood as the claim that we are not justified in believing something more specific like MWH.
In contrast to MWH, one (disputed) understanding of Kant’s things in themselves (KTIT) is:
things in themselves cause our sensory intuitions but we can never know the true character of things in
themselves.21 This understanding of things in themselves suggests a much less specific characterization of
the ‘external world’ than MWH. It may well be that this notion of things in themselves does not rule out
any of SH1-SH10. Indeed, at least on one interpretation, at least part of the purpose of the notion of things
21
I have in mind passages in Kant (1969) like those that can be found at Bxxvi, A251-2, and B306. Nothing in my
argument turns on whether this is the correct understanding of Kant or not, I’m simply referring to a common
understanding of Kant. If this is the wrong understanding of things in themselves, then imagine this is a conception
of things in themselves put forward by the imaginary (and more positive) philosopher, Kan.
25
is to rule out one important skeptical hypothesis, namely, solipsism.22 But the rejection of solipsism is not
a particularly specific hypothesis, and so it is no surprise that the rejection of solipsism is logically
compatible with MWH as well as SH1 to SH10. So, we have this relationship between the more specific
MWH and the less specific KTIT: If MWH, then KTIT. But now we may ask whether KTIT or MWH is
underdetermined. To say KTIT is undetermined should seem plausible enough to underdetermination
skeptics: the skeptical idea that solipsism might be true is familiar enough (“I could be dreaming all
this…”). But this has the embarrassing consequence that if KTIT is underdetermined, then MWH is
radically underdetermined. That is, MWH is radically underdetermined unless the underdetermination
skeptic is certain about the propositions expressing the surplus meaning of MWH in comparison to KTIT.
In particular, this would mean that the underdetermination skeptic has to be certain about (i) to (vi) above.
Conversely, if the underdetermination skeptic suggests that MWH is underdetermined, then KTIT is not
underdetermined unless the underdetermination skeptic is in a position to claim certainty about the
surplus meaning of MWH in comparison to KTIT. Again, claiming such certainty should not sit well with
underdetermination skeptics and neither should the idea that we have a priori proof that KTIT is not
underdetermined.
Moreover, this general line of thought opens up the door to a response by the dogmatist against
the underdetermination skeptic. The dogmatist may simply make MWH slightly less specific and then
escape the underdetermination argument. Take MWH* to be MWH but with no commitment to (ii)
above: that our organic brains are located in our organic bodies. So, unlike MWH, MWH* allows that our
brains might not be in our head. So, we have this relationship between MWH and MWH*: If MWH, then
MWH*. So, if MWH is underdetermined, then MWH* is not, unless the underdetermination skeptic is in
a position to be certain about the truth of the propositions that express the surplus meaning of MWH
compared with MWH*. That is, that our organic brains are located in our organic bodies.
Again, I make no commitment as to whether this is Kant’s or Kan’s view. I claim to be among the world’s
foremost scholars of the latter, not the former.
22
26
The general line of thought here is that it would be a minor miracle if MWH were exactly
underdetermined. It would have to be such that making MWH a bit more precise would lead to radical
underdetermination, and a little less precise would mean that the underdetermination argument fails. The
underdetermination skeptic is committed to the idea that MWH has hit the precise “sweet spot”. There is
no argument to this effect by underdetermination skeptics, and as I have suggested, it is quite unlikely.
Indeed, it seems we have good reason to believe that MWH, as we have formulated it, has not hit
the sweet spot. Our version of MWH is compatible with the following scenario suggested by Russell:
There is no logical impossibility in the hypothesis that the world sprang into being five
minutes ago, exactly as it then was, with a population that "remembered" a wholly unreal
past. There is no logically necessary connection between events at different times;
therefore nothing that is happening now or will happen in the future can disprove the
hypothesis that the world began five minutes ago (1921, 159).
Common sense and a naturalized world view reject Russell’s hypothesis. This means that we did not
capture everything that is important in formulating MWH in the first instance. We should add, at
minimum, that the world is more than five minutes old. If we think of the resulting hypothesis as
MWH**, then we see that:
If MWH**, then MWH.
So if it is true that MWH is underdetermined, then MWH** must be radically underdetermined (unless
we are certain that Russell’s hypothesis is false). So, a further reason to believe the underdetermination
skeptic is in no position to assert that the mundane world hypothesis is underdetermined is that it would
require a complete specification of the mundane world hypothesis and an argument that our evidence
made this completely specified hypothesis equipollent with the set of incompatible hypotheses. Since the
underdetermination skeptic has done neither, there is little reason to suppose that the mundane world
hypothesis is equipollent with some, as yet unspecified, skeptical set.
27
7. Objection: there are many MWHs
It might be thought that the whole dialectic can be skirted by simply asserting that there are more
mundane world hypotheses than the argument allows. Suppose MWH1 is MWH with the addition of a
single angel, Michael, who looks on with sympathy but does not interact with the world. MWH2 is
similar except it is Gabriel who sits passively observing reliable human perception of the mundane world.
MWH3 replaces Gabriel with Raphael, and so on. The idea being that the skeptical-dogmatist has merely
started a hypotheses arms race, and the underdetermination skeptic can generate as many MWHs as the
skeptical-dogmatist can generate skeptical hypotheses. If the skeptical-dogmatist comes up with 10, 20 or
100 skeptical hypotheses, the skeptic can come up with 10, 20 or 100 MWHs in order to restore détente,
equipollence and ataraxia.
One thing that should be said in response is that it is not clear that MWH1, MWH2, MWH3, etc.,
are really epistemologically relevant alternatives. The basic underlying epistemological model is the same
in each case. The addition of angels is a mere accretion: they play no role in undergirding the
epistemological story. Contrast this with the evil demon hypothesis. It is not an alternative to the MWH
simply because an evil demon is invoked. Suppose Descartes had asked us to imagine that there is a caged
evil demon who looks on the mundane world helplessly, but wishing he could interfere with our epistemic
lives. The threat to knowledge of MWH is gone. The addition or subtraction of such a caged demon from
the world makes no difference to knowledge of MWH. In other words, what gives the Cartesian evil
demon epistemological bite is the fact that the evil demon is said to actively interfere in our epistemic
processes. It challenges MWH at its joints, most specifically, (vi) above. So it is the epistemological
relevance that makes the Descartes’ evil demon hypothesis a competitor to MWH in a way that the caged
version of the evil demon is not a competitor hypothesis. Likewise, we can accept that MWH1, MWH2,
and so on are ontological competitors, but they are not epistemological competitors.
Furthermore, even allowing that they are epistemological competitors is not going to help the
underdetermination skeptic. For every variant on the MWH that the underdetermination skeptic suggests,
the skeptical-dogmatist may multiply skeptical hypotheses to keep pace. For example, SH1 could be
28
subdivided into SH1.1, SH1.2 and SH1.3 to include versions where Michael, Gabriel or Raphael look on
helplessly as we live out our lives in the Matrix. Similarly, SH2 can be divided into SH2.1, SH2.2 and
SH2.3 where Michael, Gabriel or Raphael look on helplessly as we live out our lives in Berkeley’s world.
This does not look like a promising means to save underdetermination skepticism.
Perhaps it will be thought that equipollence can be maintained by invoking an infinite number of
hypotheses. Imagine a new angel is added to the mundane world corresponding to every real number to
generate an infinite number of MWHs. Every time the skeptical-dogmatist offers another skeptical
hypothesis, the underdetermination skeptic can offer, ad infinitum, a MWH variant from the infinite set.
This will ensure, so the objection goes, that the set of MWHs and skeptical hypotheses are equipollent
with exactly an infinite number each.
This move is to no avail, since the underdetermination skeptic must face this dilemma: either the
underdetermination skeptic invokes equipollence on the basis of the probability of individual hypotheses
or on sets of hypotheses. Taking the former first, the probability of any sample point in a continuous (i.e.,
infinite) sample is 0.0, so the probability that any individual variant of MWH is true is 0.0 (Hazewinkel
1995). That is, if the set is infinite, then the probability that MWH1 is true is 0.0, the probability that
MWH2 is true is 0.0, and so on. Of course, the same reasoning would apply to each skeptical hypothesis:
the probability of each is 0.0. Still, this result would be at least partially congenial to the skepticaldogmatist, for it would entail an even stronger conclusion than RUC1: we can be certain that each
hypothesis—mundane or skeptical—is false. Obviously, the skeptical-dogmatist would have to give up
the idea that some skeptical hypothesis is probably true, that is, RUC2.
More plausibly, the underdetermination skeptic might invoke the usual way of speaking about
non-zero probabilities in continuous sample spaces: probability density functions. Here are two ways we
could write probability density functions for the infinite number of sample points in the sample space of
real numbers between 0 and 1. We could divide the sample space in half: there is a 0.5 probability of
selecting a number larger than 0.5 and less than 1; and a 0.5 probability of selecting a number less than
0.5 but greater than 0. The second possibility is to divide the sample into thirds as follows: a 0.33
29
probability can be assigned to the real numbers between 0 and .33; a 0.33 probability can be assigned to
the real numbers greater than .33 and less than .66; and a 0.33 probability can be assigned to the real
numbers between .66 and 1.0.
The underdetermination skeptic’s assertion that there are an infinite number of MWHs does not
help us decide which probability density function to apply: For in each segment just defined, there are an
infinite number of sample points. There are an infinite number of real numbers between 0.0 and 0.33 just
as there are an infinite number of real numbers between 0.0 and 0.5. So, the appeal to an infinite number
of hypotheses is not sufficient to decide the correct probability assignment.
Once we see that considerations other than the fact that there are an infinite number of hypotheses
will need to be adduced to decide on the correct probability function, we return to very familiar territory.
Similar lines of reasoning used in section 6 are relevant. We can ask, as we did in 6.1, about the
probability of the discrete parts of MWH. If the underdetermination skeptic claims the probability density
function of the set of MWHs is 0.5, then the average probability of each subcomponent ((i) to (vi)) will
have to be approximately 0.9. If the average probability of the subcomponents is less than about 0.9, then
the set of MWHs is radically underdetermined. The former has the underdetermination skeptic sounding
very close to a dogmatist about the subcomponents; the latter has the underdetermination skeptic
conceding to the skeptical-dogmatist. We may note too, as we did in 6.2, that if the underdetermination
skeptic assigns a 0.5 probability function to the set of home field hypotheses, then the Matrixians and
Berkeleyians are entitled to the same assumption. But this leads to inconsistencies, including a combined
1.5 probability of all the home field hypotheses being true. Finally, the argument of 6.3 is relevant: if the
underdetermination skeptic asserts that a 0.5 probability ought to be assigned to the infinite number of
MWHs, then it will follow that a less specific hypothesis about reality, like Kantianism, must not be
underdetermined. But it is difficult to see how an underdetermination skeptic would be in any position to
assert this. So, the appeal to an infinite number of MWHs is of no help to the underdetermination skeptic:
it is possible that MWH is radically underdetermined, and that there are an infinite number of MWHs.
30
8. Some Consequences
One consequence is that a certain type of skepticism is not viable. To see what is at issue,
consider first Jonathan Vogel’s useful distinction between ‘domestic’ and ‘exotic’ skepticism. Domestic
skepticism is
…concessive, in that it doesn’t contest the legitimacy of the epistemic principles we
employ. It is also dangerous in the sense that it would be deeply unsettling, or worse, if
we have no knowledge of the world, according to our own accepted view of what
knowledge is and what it requires (2005, 73-4).
Vogel describes ‘exotic skepticism’ as the view “Someone might contest not only our ordinary judgments
that we have knowledge of the world, but also the legitimacy of the principles on which we rely in
making that judgment (2005, 74).” What is at issue here is domestic skepticism. Following Vogel,
domestic skepticism accepts the underdetermination principle as a condition for justified belief or
knowledge. Once we see that there must be numerous equipollent hypotheses to MWH, according to the
underdetermination skeptic’s own premises, we are led to a stronger conclusion than domestic
underdetermination skeptics have allowed, namely, the view that MWH is probably false. If the argument
is correct, then domestic underdetermination skepticism is not viable, which reduces our original field of
three candidates down to two: skeptical-dogmatism and dogmatism.23
Dogmatists should be pleased to hear about the demise of domestic underdetermination
skepticism, but skeptical-dogmatism poses its own unique challenges to dogmatism. To illustrate I would
like to canvas, albeit very briefly, three points of contact.
The first has to do with the fact that RUJP is weaker than UJP. To see the relevance, consider that
it has been suggested that one way to deal with traditional underdetermination arguments is to reject UJP
in favor of a less stringent “Conservative Principle”:
23
I am ignoring the possibility that the domestic underdetermination skeptic might retreat to exotic skepticism.
31
CP: If q is a competitor to p, then a subject S is not justified in believing p if q has more
epistemic merit (for S) than p (Foley 1983). 24
Rejecting UJP for CP appears to be sufficient for undermining the traditional underdetermination
argument. For even if it is granted that MWH is equipollent with some skeptical competitor in the minor
premise, CP allows that belief in MWH may still be justified. However, RUJP and CP are jointly
consistent. Hence, rejecting UP in favor of CP will not directly challenge the argument for the radical
underdetermination argument for skeptical-dogmatism. This foregrounds the interesting fact that the
radical underdetermination argument is able to get to a stronger conclusion than underdetermination
skepticism with a weaker premise. Dogmatists who had hoped to challenge underdetermination
arguments by rejecting UJP in favor of CP will either have to abandon or modify the CP strategy.
A second point of contact turns on the strength of favoring evidence required by dogmatists to
thwart underdetermination arguments. To illustrate, consider the “abductionist response” to
underdetermination skepticism briefly discussed above. 25 As we noted, one version of the argument is
that MWH has the explanatory virtue of simplicity over a skeptical competitor like the thought that we
might be brains-in-a-vat (SH4). In other words, simplicity is understood as evidence for truth (Swinburne
1997).26 In the case of a single competitor, there is no need to discuss in any detail exactly how much
evidential weight simplicity provides. So long as we grant that MWH is simpler than (say) SH4, and
simplicity offers some positive amount of evidential weight, this is enough to show that MWH and SH4
are not equipollent. However, when there are two or more skeptical competitors, then the issue of the
amount of evidential weight added by simplicity becomes more serious. For suppose we grant that MWH
Hazlett has a similar principle which he calls ‘security’: “S’s justified hinge belief that p is defeated only if S has
sufficient reason to believe ~p. (2006, 200).
25
A good short history of this reply can be found in Beebe (2009) who claims that this response can be found in the
writings of Locke, Russell, Goldman, Vogel, and Bonjour among others.
26
It might be thought that the skeptic will question whether simplicity is evidence for truth, but recall that it is
domestic skepticism that is at issue. Vogel argues, for example, that inference to the best explanation is part of the
package of epistemic principles that a domestic skeptic cannot challenge (but, of course, an exotic skeptic might)
(Vogel 2005). I argue in a related paper that questioning simplicity as evidence for truth is not a particularly
attractive option for the underdetermination skeptic. Basically, since there are so many more complex hypotheses
than simple hypotheses, we should endorse Occam’s Beard: other things being equal, it is more likely that a
complex hypothesis is true. I show that the underdetermination skeptic needs something like Occam’s Razor to
thwart Occam’s Beard and skeptical-dogmatism.
24
32
is simpler than SH4 and SH2, and simplicity is evidence for truth, then P(MWH/e) > P(SH4/e) and
P(MWH/e) > P(SH2/e). Clearly, it does not follow that P(MWH/e) > P(SH4/e or SH2/e). So, merely
allowing that simplicity is evidence for truth, and granting MWH is the simplest hypothesis, is not
sufficient to undermine skeptical-dogmatism. The obvious thought is that the abductionist strategy could
be modified to say that simplicity adds at least enough evidential weight to outweigh the probability of
the skeptical set. The point here is not that it is impossible for the dogmatist to modify this argument, only
that the usual formulations of the argument must be modified. So dogmatists must rethink this strategy
too.
A third point of contact is with perhaps the most common form of dogmatism today: externalism.
To see this, it will help us to have just the barest sketch of the externalists’ response to skepticism. A
common complaint against skeptical arguments is that the skeptics’ standards for knowledge are too high,
they are “inhuman”; and that with more “human-size” epistemic standards we need not accept the
skeptic’s denial of much of our everyday knowledge (Harper 2010). A common means presently to
diagnosis the complaint about “inhuman” standards is to say that skeptics presuppose an internalist
conception of knowledge.27 “The internalist,” according to Chisholm, “assumes that, merely by reflecting
upon his own conscious state, he can formulate a set of epistemic principles that will enable him to find
out, with respect to any possible belief he has, whether he is justified in having that belief (1989, 760.)”28
According to the externalist, it is not necessary for knowledge that the epistemic principles be available to
reflective consciousness. Consequently, if some set of external conditions are satisfied (e.g., reliability,
sensitivity, safety, epistemic virtue, proper functioning29), then we have externalist knowledge of the
mundane world. If the underdetermination skeptic tries to show that the antecedent is false by claiming
the consequent is false, then the externalist has a seemingly powerful rebuttal: the skeptic can only show
27
Pritchard does a nice job canvassing the various moves in this debate (2005a). Note: I am not saying that the only
thing externalism has going for it is its ability to deal with skepticism. However, even if externalism is
independently motivated other than by its ability to deal with skepticism, the ability to deal with skepticism is often
a claimed benefit.
28
For sake of brevity, I shall ignore other conceptions of internalism that don’t require reflective access, for
example, Conee and Feldman (2004)
29
See Pritchard (2005a) for an overview of these forms of externalism.
33
that we fail to have internalist knowledge, not externalist knowledge. And so, the conclusion that we lack
knowledge is based on an illicit equivocation on the type of knowledge (internal or external) involved, or
simply begs the question by assuming that internalist knowledge is required.
Many externalists allow a “non-substantive” (Pritchard 2012, 57) internalist condition: they allow
reflectively available defeaters, even misleading defeaters, to undermine external knowledge. So, for
example, they may maintain (1) it is necessary that belief, if it is to be converted to knowledge, be formed
reliably, sensitively, safely, virtuously or proper functionally; and (2) it is necessary that knowers do not
(internally) justifiably believe that the belief was formed in a non-reliable, non-sensitive, non-virtuous or
non-proper functioning manner (A. Goldman 1979, 1986; Nozick 1981; Plantinga 1993; Hazlett 2006 and
Bergman 2006).30
Skepticism and skeptical-dogmatism part company on the issue of whether underdetermination
considerations provide a defeater to MWH. Since skeptical-dogmatism says that MWH is probably false,
it provides a means to generate an internal defeater to putative external knowledge. For example, to the
putative knowledge claim that there is a material table in front of me at this very moment which bounces
photons and sends information to my brain via my eyes, dogmatic-skepticism offers a defeater: it is much
more likely that some explanation other than MWH is probably true as to why it appears that there is a
material table in front of me. 31 From the skeptic’s point of view, as we noted above, thinking that we
have justified reason to suppose that MWH is probably false (rather than unjustified) is a form of
dogmatism. It is true that underdetermination skeptics raise alternative hypotheses to MWH, but they do
not claim that alternate hypotheses to MWH are justified, hence alternative hypotheses are not offered as
defeaters by skeptics.
30
For review of the no defeater condition in relation to externalism see Greco (2010, Chapter 10).
It may be that accepting underdetermination skepticism is not sufficient for domestic skepticism. If one accepts
the semantic externalism of Putnam (1975, 1981) and others, then many of our everyday statements may come out
true no matter what metaphysical hypothesis is true. For example, if I am a brain-in-a-vat and semantic externalism
is true, then ‘hand’ will refer to a computer generated image of a hand, and in Berkeley’s world ‘hand’ will refer to
immaterial body parts and so on (Chalmers 2009). This line of thought would also seem to take much of the sting
out of skeptical-dogmatism; however, it is beyond the scope of this paper to address these interesting issues.
31
34
In light of this, the choice for the externalist seems to be to either jettison even the nonsubstantive internal condition on knowledge, or join the dogmatic internalist in looking for a rebuttal to
skeptical-dogmatism. I suspect neither option will look particularly appealing to externalists. The former
seems to allow that we can know P even though we have reflectively available justification for probably
not-P.32 The latter option seems to invite the externalist to engage in old school epistemology: a quagmire
that many externalists hope to escape.
I have rapidly sketched three points of contact. I am not suggesting (here at least) that they are
sufficient to spell doom for dogmatism. Rather, I am making the much more limited claim that it would
be wrong to conclude that underdetermination skepticism and skeptical-dogmatism challenge dogmatism
in exactly the same way. Rather, dogmatic-skepticism may provide a unique challenge to many forms of
dogmatism about MWH, both internally and externally conceived.33
32
33
But see (Alston 1989, 172-182).
My thanks to Peter Hutcheson, Danny Scoccia and several hundred anonymous reviewers (one at this journal).
35
References
Alston, William P. 1989. Epistemic Justification: Essays in the Theory of Knowledge. Cornell University
Press.
Beebe, James. 2009. “The Abductivist Reply to Skepticism.” Philosophy and Phenomenological
Research 79 (3): 605–636.
Bergman, Michael. 2006. Justification Without Awareness: A Defense of Epistemic Externalism. Oxford:
Oxford University Press.
BonJour, Laurence, and Ernest Sosa. 2003. Epistemic Justification: Internalism Vs. Externalism,
Foundations Vs. Virtues. Blackwell Publishing.
Brueckner, Anthony. 1994. “The Structure of the Skeptical Argument.” Philosophy and
Phenomenological Research 54 (4): 827–835.
Chalmers, David. 2009. “The Matrix as Metaphysics.” In Susan Schneider ed. Science Fiction and
Philosophy: From Time Travel to Superintelligence: 33-52. Wiley Blackwell.
Chisholm, R. M. 1989. Theory of Knowledge. Prentice-Hall Englewood Cliffs, NJ.
Conee, Earl, and Richard Feldman. 2004. Evidentialism: Essays in Epistemology: Essays in
Epistemology. Clarendon Press.
Davidson, Donald. 2006. The Essential Davidson. Oxford University Press.
Descartes, René. 1993. Meditations on First Philosophy in Focus. Routledge.
Foley, Richard. 1983. “Epistemic Conservatism.” Philosophical Studies 43: 165–182.
Fumerton, Richard. 1992. “Skepticism and Reasoning to the Best Explanation.” Philosophical Issues 2:
149–169.
———. 2005. “The Challenge of Refuting Skepticism.” In Contemporary Debates in Epistemology.
Malden: MA.
Goldman, Alan H. 2007. “The Underdetermination Argument for Brain-in-the-vat Scepticism.” Analysis
67 (1): 32–36.
Goldman, Alvin. 1979. “What Is Justified Belief?” 1979: 1–23.
———. 1986. Epistemology and Cognition. Harvard University Press.
Greco, John. 2010. Achieving Knowledge: A Virtue-theoretic Account of Epistemic Normativity.
Cambridge University Press.
Hájek, A. 2007. “My Philosophical Position Says ‘p’and I Don’t Believe ‘p’.” Mitchell S. Green & John
N. Williams (eds.) Moore’s Paradox: New Essays on Belief, Rationality, and the First Person:
217. Oxford University Press.
Harper, A. S. 2010. “Fallibilism, Contextualism and Second-Order Skepticism.” Philosophical
Investigations 33 (4): 339–359.
Hazewinkel, Michiel. 1995. Encyclopedia of Mathematics. Dordrecht: Kluwer Academic.
Hazlett, Allan. 2006. “How to Defeat Belief in the External World.” Pacific Philosophical Quarterly 87:
198–212.
Hilary, Putnam. 1975. “The Meaning of ‘Meaning’.” Mind, Language and Reality: 215–271.
Kant, Immanuel. 1969. Critique of Pure Reason. Bedford Books.
Keynes, John Maynard. 2004. A Treatise on Probability. Dover Publications.
Kuhn, T. S. 1977. The Essential Tension. Selected Studies in Scientific Tradition and Change. Vol. 1.
Chicago University Press.
Mates, Benson. 1996. The Skeptic Way. New York: Oxford University Press.
Nozick, R. 1981. Philosophical Explanations. Belknap Press.
Plantinga, Alvin. 1993. Warrant and Proper Function. Oxford University Press, USA.
Pritchard, Duncan. 2005a. Epistemic Luck. New York: Oxford University Press.
———. 2005b. “The Structure of Sceptical Arguments.” Philosophical Quarterly 55 (218): 37–52.
36
———. 2012. Epistemological Disjunctivism. Oxford University Prss.
Pryor, James. 2000. “The Skeptic and the Dogmatist.” Nous 34: 517–549.
Putnam, Hilary. 1981. Reason, Truth, and History. Cambridge University Press.
Russell, B. 1921. The Analysis of Mind. Psychology Press.
Sklar, L. 1975. “Methodological Conservatism.” The Philosophical Review: 374–400.
Sorrenson, Roy. 2004. “Commercial Applications of Pyrrhonianism.” In Pyrrhonian Skepticism, 208–
232. Oxford University Press.
Swinburne, R. 1997. Simplicity as Evidence of Truth. Marquette University Press Milwaukee, Wisconsin.
Vogel, Jonathan. 1990. “Cartesian Skepticism and Inference to the Best Explanation.” Journal of
Philosophy 87 (11): 658–666.
———. 2005. “The Refutation of Skepticism.” In Contemporary Debates in Epistemology, 72–84. New
York: Blackwell.
Winkler, K. P. 1989. Berkeley: An Interpretation. Clarendon Press Oxford.
37