IV.—INFERENCE FROM THE KNOWN TO
THE UNKNOWN.
By J. WATLING.
In this paper I want to consider two arguments which lead either to scepticism or to phenomenalism:
either, that is, to the belief that we do not really know about some matter which we are generally
supposed to know about or to the belief that statements about that matter have a meaning very different
from the meaning they are generally supposed to have. One of the arguments is the familiar one that
Hume used to throw doubt upon our knowledge of the future: it is generally used to support scepticism
about the possibility of our knowledge of the future, and of physical objects, but it supports equally well
scepticism about our knowledge of other matters. The other is the argument from the Verification
Principle. It has been used to support scepticism about the past, the present, the minds of others, and
about what would have followed had some event happened which did not happen. It too could have a
wider application. Both of these arguments try to show that we cannot possibly have knowledge of
matters of some kind but it would follow that we could not even talk meaningfully about these matters.
Both arguments begin by trying to prove that it is logically impossible for us to have knowledge of
certain propositions which we suppose ourselves to know and then go on to try to show that we cannot
even express these propositions. The arguments try to show that a large class of sentences which we
suppose meaningful arc either meaningless or else have a meaning of a rather peculiar kind. I shall deal
first with Hume’s argument.
The First Argument
It is sometimes held that arguments such as those of Hume and Berkeley1 which seek to prove
that it is impossible for us to have knowledge of the future, or of physical objects, rest on an
unreasonable and groundless assumption: that a conclusion can be known on the basis of known
evidence only if that evidence entails the conclusion. The sceptical arguments err, it is said, in insisting
that the evidence entail the conclusion whilst it is clear that it need only factually imply the conclusion.
The way out of these doubts is to see that this demand is being made and to see that it is unreasonable.
1
E.g., Enquiring concerning the Human Understanding, Section IV. Principles of Human Knowledge,
Part 1, Para. 18.
1
But it is not true that the sceptical arguments merely assume that to give knowledge of the
conclusion evidence must entail the conclusion, for the arguments are directed to proving that this
must be so.
The arguments run: knowledge of our own ideas is not by itself sufficient for knowledge of
physical objects that are independent of our minds therefore we can have no knowledge of physical
objects, or knowledge of the past is not by itself sufficient for knowledge of the future therefore we can
have no knowledge of the future. They are used in situations where it seems obvious that we do in fact
base a part of our knowledge entirely upon other more certain knowledge and they try to show that the
basis is not adequate to justifying the conclusions. I think that the form of the arguments is made clear
by the following example: Suppose it is asserted that we do have knowledge of the future because we
base this knowledge upon our knowledge of the past: we know the future because we have good
evidence for our assertions about it, evidence about the past. Then in order to argue from the evidence
about the past to the conclusion about the future we must assume, either implicitly or explicitly, the
truth of some implication. It may be that we never consider the implication we assume, passing directly
from the assertion of the evidence to the assertion of the conclusion, nevertheless the implication we
employ plays as large a part in determining the conclusion at which we arrive as does the evidence from
which we begin. It is as important to travel in the right direction as it is to start from the right place. If
the implication is logical, then the evidence will entail the conclusion and our assertion about the future
will be based entirely, so far as empirical facts are considered, upon our evidence about the past. If the
implication is empirical, then the conclusion about the future will not be based entirely upon the
evidence: other empirical facts will have been assumed. If the implication is not given a justification, as
it cannot be on our assumptions if it is not itself a fact about the past, then the conclusion about the
future cannot count as knowledge since it depends upon unsupported assumptions. The conclusion
depends equally on a number of facts: surely it is irrational to insist that some of these facts be justified
and allow others to be assumed out of hand. It is as irrational to demand rigorous conditions of the
evidence and none of the step from evidence to conclusion as it would be to demand rigorous
conditions of the step from evidence to conclusion and none of the evidence. Therefore the conclusion
about the future can be known only if it is entailed by evidence about the past.
But, if this is the case, then the conclusion says nothing that the evidence does not say. If the
evidence consists only of facts about the past, then so does the conclusion. Therefore from a knowledge
of past facts alone it is impossible to obtain knowledge of the future, logically impossible, because if the
conclusion is solely based upon evidence about the past, then it is a conclusion about the past and it
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would be contradictory to suppose that a conclusion about the past was also a conclusion about the
future.
This argument seems to me to be valid: it seems to me that it establishes not only that if we
have knowledge of the future because we base our assertions about the future entirely upon our
knowledge of the past, then we do not have knowledge of the future; but also that if our assertions
about the future can be called knowledge only if they are justified by known evidence, which our
knowledge about the past provides, then our assertions about the future can be called knowledge only if
they are entirely based upon known evidence, though of course this need not be evidence about the
past. The argument establishes that the reasons for supposing that “justified by good evidence “ is a
necessary condition for an assertion to count as knowledge are also reasons for supposing that “entirely
justified by good evidence” is a necessary condition for an assertion to count as knowledge. If “based
upon good evidence” is necessary, then so is “derived from good evidence by a justified and sound
inference”.
Of course to say that a conclusion is entailed by the evidence upon which someone bases his
assertion of the conclusion is not the same as to say that he derived his conclusion from the evidence by
a justified logical inference. The second may entail that the conclusion is known but the first does not.
A man may accept a conclusion because he has derived it from evidence which he knows to be true and
it may in fact be the case that his evidence entails his conclusion and yet he may not know the
conclusion, for he may have deduced the conclusion from the evidence by a deduction which is faulty
but accidentally correct. That the conclusion is entailed by known evidence is not a sufficient condition
for knowledge.
The argument establishes that if our assertion of a statement about the future is to be called
knowledge because it is based upon our knowledge of the past, then it must be based upon no other
facts except those about the past, it must be derived from these with the help of no other facts but those
about the past, and only justified logical inferences may be used in the deduction. It follows that it is
contradictory to suppose that we have knowledge of the future because our assertions are based upon
knowledge of the past.
Yet how can we justify our knowledge of the future except by showing that it is based upon
what is much more certain, upon our knowledge of the present and past? How can we justify our
knowledge of the minds of others except by showing how it is impeccably derived from our knowledge
of their behaviour and of our own minds? How can we justify our knowledge of the properties of
physical objects except by showing how it is obtained from our knowledge of our own sensations? For
we do obtain our knowledge of the future from our knowledge of the past, we do make our judgments
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about what other people are feeling from our observations of their behaviour, and we do base our
opinions of the properties of physical objects upon the sensations that we experience.
Refutation of the Argument
If there is any fault in the sceptical argument it must lie in the assumption that our assertions
about the future count as knowledge because they are based upon other facts which are more certain. It
is this assumption that I want to challenge.
Consider knowledge which is not knowledge of facts: a horse knows its way home, Smith
knows the way to manage his wife: Jones knows when to stop. The facts that the horse finds its way
home, that Smith gets his own way, and that Jones stops, all on some particular occasions, would not be
sufficient to justify the assertions that they knew how to do all these things, but they would support
them. They would support them because they are part of what must happen if the horse is habitually to
find its way home, if Smith is invariably to be one too many for his wife, and if Jones is never to provide
us with too much of a good thing. And the habitual successes are very good support for the assertions
that they know how to do these things because they support the statements that they possess a certain
ability. Of course a series of successes is neither necessary nor sufficient for a person to have an ability,
he may never have the chance to exercise his skill, or he may have beginner’s luck, but it is strong
support for this. The question of what evidence the horse could bring to support his belief that here he
should turn right and here left, or what evidence Smith could bring to prove that kindness melts the
hardest heart, is not peculiarly relevant to whether they possess the skills of finding their way home or
getting their own way: it is certainly not logically relevant to it, for it is not probable that many horses
that can find their way home know what signs they take account of or that many people who can
influence the behaviour of others know of what psychological laws they make use. Even discussions of
the signs by which the horse is unwittingly guided, or the cues upon which Smith acts when he attempts
to control someone’s behaviour, or the laws upon which their success depends, are not logically
relevant to whether they possess the ability to find their way home or to control other people. These
discussions are factually relevant, if we could find no causes governing the horse’s behaviour we should
be inclined to doubt whether he did possess the ability to find his way home, but even if we do
sometimes accept that the fact that we can find no explanation of how he did it is better evidence that
he does not know his way home than the fact that he is invariably successful is evidence that he does
know his way home, nevertheless that there is no explanation of his ability does not entail that he does
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not have the ability. The ability to perform a task, the explanation of the ability, and the performance of
the task are all different things.
All this is well recognized for those abilities that G. Ryle has called “knowing how”. I want to
suggest that it is just as true for the ability of “knowing that”. Knowing that an event of some kind is
going to happen is just as much a knowing how to do something as is knowing how to catch elephants:
it is an ability of a different kind but it is none the less an ability. “Knowing that” is a kind of “knowing
how” just as knowing how to catch elephants is a kind of “knowing how”: the difference lies in the task
to be performed. To know that some fact is the case is to know how to tell the truth about matters of a
certain kind, given, of course, the further ability to express propositions in some language. A person
who knows that some event is going to happen is a person who, if he could talk, could correctly predict
both that event and other events of its kind. Knowing that something is the case is not the same as
knowing how to describe correctly, for an animal may know facts without being able to express them in
language, but it is the ability to describe correctly given the ability to describe at all. To know facts of a
certain kind is to know how to pick out true propositions from false.
What is true about knowing how to perform other tasks is true about knowing how to
recognize true propositions, about knowing how to tell the truth: the ability is not logically dependent
upon the way it is acquired or upon how it is exhibited. In particular whether a person knows
propositions which are evidence for some proposition is independent of whether he knows that
proposition itself. The importance of this analysis is that it puts emphasis on the abilities and behaviour
of people who believe propositions rather than on some process for guaranteeing the truth of the
propositions themselves.
The flaw in Hume’s argument is now apparent. His proof that knowledge of the future was
impossible rested on the assumption that good evidence, in the form of statements about the results of
present and past observations, was logically necessary for knowledge; if this is incorrect and if, as I have
argued, the only question that is logically relevant to whether a person knows facts of some kind is
“Could he tell the truth about them if he could speak?”, then Hume’s proof that we never have evidence
about the present that is a sufficient basis for statements about the future does not establish that we can
never know the future.
The sort of example that is conclusive against the view that an assertion can only count as
knowledge if it is based upon good evidence is the following:
Suppose that I walk softly about behind a high wall and that someone else walks on the other
side and tries to say where I am. I find to my astonishment that he is always right: when he says “Now
you are here”, then I am there, but I do not tell him that he is right, since I do not wish to encourage
5
him. If he kept this up, then I could not avoid the admission that he knew where I was, although he
could not see or hear. Now I have confirmed a good many of his predictions, but he has confirmed
none of them. Therefore he knows where I am without having any evidence whatsoever.
Therefore there is no good ground for saying that a person cannot know the future, or that
scientific laws do not enable us to know that when an event of kind A occurs, then an event of kind B
will follow. Nor is our knowledge in any situation restricted to those facts which it is logically possible
to verify whilst we remain in that situation. For it is not true that people know facts only when they
have made predictions and verified them: they need only the ability to make correct predictions. These
predictions need never be verified nor ever made. Grazing animals know when beasts of prey are near
by getting wind of them and we do not say that they do not know this just because they are not silly
enough to risk being eaten in order to verify the fact. People living today may know how Elizabethan
English was spoken even though no one can now hear it: perhaps present day students of phonetics do
not know this, what they believe may be wrong, but it is logically possible that they do know.
It is clear too why it is that evidence may be good evidence for a conclusion without entailing
that conclusion. A person who takes smoke to be a sign of fire will know of the presence of a fire when
he observes smoke. The truth of the law “No smoke without fire” ensures that anyone who accepts it,
and acts upon it, will never say “Fire” on the occasion of smoke and be wrong. To know the conclusion
it is sufficient to know the particular evidence and to accept the law relating this evidence to the
conclusion: for this is sufficient to give the ability to make correct predictions. The law itself need not
be known, it need be accepted only.
The answer to questions such as “How can this evidence provide knowledge, for how can it
guarantee the conclusion?”, and “How can this evidence provide knowledge, for the conclusion cannot
be read in the evidence; knowing the conclusion and knowing the evidence are two different things”, is
“It can guarantee the conclusion because anyone who knows the evidence and accepts the connection
between the evidence and the conclusion will have the ability to make correct assertions about the facts
which the conclusion states, and this is what is required for knowledge.”
Fortune tellers, almanac writers, and astrologists do not have knowledge of the future. But
neither the fact that they do not use correct “scientific method” nor the fact that they do not make their
assertions on what is accepted as good evidence by “the scientists of our culture circle,” entails that they
do not know the future. Certainly the methods they use could not give them knowledge but this is for
the factual reason that the methods do not work, not for the logical reason that any predictions made by
these methods would not count as knowledge. We say they do not know the future because we do not
believe that they have the skill to which they pretend. If crystal gazing did enable its practisers to foretell
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the future, then we should have to admit that what was seen in crystals did provide good evidence for
future events.
I have argued that accepting a general law ensures that we have the ability to make correctly
those particular inferences which may be deduced from the law; therefore accepting the law ensures
that we know the truth of the particular inferences which may be obtained from it. Since we only
require laws for the sake of the particular inferences that they justify, then it is not important, for the
purpose of establishing that science does provide us with knowledge, to establish that the laws can be
known in any other sense than that of being accepted. There seems, in fact, to be one use of the
sentence “This law is known” which does entail no more than that the particular inferences obtainable
from the law are known; but it may be that the sentence is also used to assert a stronger proposition
which entails, perhaps, that the person in question has the ability to pick out, from a class of hypotheses
of a certain character, those which are laws. It is presumably for this reason that some writers, R. B.
Braithwaite for example, do not agree that a law is known unless it is deduced from other laws.
It scarcely needs arguing that the relation between evidence for an hypothesis and the
hypothesis itself is not a factual relation. If it were, then to know that it held would be to know a law
having the evidence as antecedent and the hypothesis as consequent. The inductive argument is neither
factually nor logically valid. What is true is that some kinds of evidence have an effect on a person
considering an hypothesis, inclining him to accept or reject it. The study of what facts are taken as
evidence for an hypothesis is a part of human psychology, a part of the psychology of learning. When
we ask “Has he good evidence for his assertion?” we are asking whether he has had the opportunity to
learn about the facts in question. When we doubt someone’s assertions about Africa and say “How can
he know that, he has never been in Africa?” we are pointing out the absence of a causal connection
between the situation and his beliefs about the situation. Of course when a man has knowledge in a
particular situation we tend to say that he has evidence in that situation: as remembering is said to be
having evidence for past events.
That someone accepts a causal law entails that he knows how to infer the existence of some
condition from the existence of other conditions. Scientists try to discover causal laws just because this
entailment holds, because laws provide knowledge; no a priori proof of its laws is necessary as a basis
for science. To have scientific knowledge is to possess an ability, an ability in the use of propositions
which leads to other more practical abilities. The distinction between scientific knowledge and recipe
book knowledge is that scientific knowledge is obtained from a general principle whilst recipe book
knowledge is not. Scientific knowledge might be impossible for two reasons: it would be impossible if
there were no casual laws and it would be impossible if we were too stupid to discover those which
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there were.2 There cannot but be true generalizations, but though a man who accepts a true
generalization will never be misled by it into making mistaken inferences about what has been, is, or
will be, yet he will not necessarily know the truth of the correct conclusions at which he arrives. For he
may be right about what has been, is, and will be and wrong about what would have been or about what
would be. If this is so, then had things happened in a different fashion he would have arrived, not at
true conclusions, but at false ones, and so the correct inferences which he in fact makes are the result of
chance and not of knowledge. For example, suppose that someone like Scythrop in “Nightmare Abbey”
writes a philosophical treatise which has the misfortune to be read by only one person. Of it the
generalization might hold “All the readers of this work are women”- and anyone accepting this
generalization would not make a false statement about what was actually the case. Nevertheless
accepting this generalization might very well have led him astray, so that he would have been right
merely by accident. Had he used a law and not a generalization, then he would not have been right
merely by accident. It is for this reason that scientists wish to discover causal connections rather than
generalizations. It is true, then, that the existence of scientific knowledge depends upon the fact that
causal laws hold, but it does not follow from this, nor is it true, that the existence of scientific
knowledge depends upon the a priori assumption that causal laws hold: it is just the business of
scientists to find out if any do hold and, if some do, what they are.
But although the discovery of a law provides knowledge, yet it is possible for a person to have
knowledge without accepting any laws, for it is possible that he should have the ability to make correct
assertions in situations of a certain kind and yet not make those assertions on the basis of inference
from other propositions. There is nothing contradictory in supposing that we have non-inferential
knowledge of future events.
A. J. Ayer has pointed out3 that the problem of how can we know the future is like that of how
can we know about the minds of others. The inferences upon which our knowledge of the minds of
others is based are accepted, it is said, upon evidence which falls far short of the standards by which
scientific hypotheses should be judged. One sort of inference upon which this knowledge is said to be
based is the argument from analogy which may be described in this way: One person (the person
employing the argument) observes that he has certain physical and psychological properties, in
particular that certain psycho-physical laws are true of him, such as that when he is pinched he feels a
pain, when he is in a room where the air is not circulating he sometimes loses consciousness, and so on.
More than this it seems to him that his conscious experiences play an important role in determining his
2
The reason why most scientific laws are simple, if this is indeed so, is that human beings are not
clever enough to discover the complicated ones.
3
Theoria, Vol. XIX, 1-2; 1953.
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behaviour, though whether they do is open to serious doubt. He observes that another person shares
many of his physical, physiological, and psychological properties and from this he infers that the
psycho-physical laws that are true of himself are true of the other person: he infers that pinches cause
pain to the other and that the other’s behaviour is partly determined by conscious experiences. To make
an inference of this kind is to use the argument from analogy. It would be to argue from analogy, for
example, to infer from the fact that two people shared many important properties to the fact that if one
of them has conscious experiences, then the other has; or that the law which associates behaviour with
conscious experience in one person may be generalized to apply to any person who sufficiently
resembles the first. Both these arguments may be criticized. The first holds that since two sets of
properties have been found together in one single case, then they will be found together in many other
cases. No scientist would accept an hypothesis on only one test, so how can we accept such reasoning?
Would it not justify the conclusion that the second man has all the properties of the first? The second
argument, depending upon an hypothesis which has been confirmed a great many times, might seem to
be on surer ground; but when the hypothesis is extended from one person to another a great many
factors are supposed irrelevant to having conscious experiences which may very well be relevant. No
scientist can be criticized for failing to test his hypothesis under all conditions, but he may fairly be
criticized for not carrying out tests under conditions which may well be relevant. Consciousness, as
anyone may verify, is dependent upon brain conditions which are easily disturbed, by a blow on the
head, for instance, or by an overdose of a drug. How can we feel confident that the brain of the second
person is maintained in the same condition of critical balance as that of the first?4
Both these criticisms make the same point: the hypotheses employed have not been tested in
sufficiently varied conditions. Further I can never confirm any inference to the existence of conscious
experiences of another person by verifying any of the predictions which I make. If no hypothesis can be
known without its predictions being verified on at least some occasions, then no hypothesis justifying
inferences to the experiences of another person can be known.
Argument between those who claim that evidence for these hypotheses is good and those who
claim that it is not good can go on interminably: for no definitive standards of evidence exist. Those
claiming that the evidence is good may reasonably point to the fact that there are always factors whose
influence on a certain occurrence still remain to be tested; they may argue that whether the influence of
a factor has not been investigated through lack of time or whether it has not been investigated because
of the impossibility of changing one’s date of birth is immaterial: what is relevant is that some factors
always remain whose influence has not been determined. Why not a Next Event problem as well as an
4
M. Shearn, Proceedings of the Aristotelian Society, 1949-50.
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Other Minds problem? Cannot the same demands for stricter standards of evidence be made for any
non-logical inference?5
Such a discussion soon becomes recognizable as one which, as John Wisdom puts it, has gone
on too long. It is of the very nature of philosophical problems he suggests, that they are ordinary
questions to which philosophers, refusing to accept the ordinary methods of deciding them, bring an
inexorable doubt. Evidently it is possible to demand such rigorous standards of evidence that no one
can know anything but his own condition at that time, for at that time he is unable to verify the
predictions of any of the laws which might tell him about the past, the future, the invisible, or the minds
of others: too strict a standard of evidence leads to solipsism of the present moment and too lax a
standard will permit any ill founded hypothesis to count as reasonable. But it is one thing to suggest
that an argument has gone on too long, another to explain why it has done so. The reason for the
persistence of this one lies in a mistake about the relation of good evidence to knowledge. Philosophers
tackling the problem are rather like men attempting to judge the artistic value of pictures by their price.
Such a group might discuss at great length the price standards to be adopted, always puzzled by
divergences between their standards and criteria which they apply but do not recognize. They would
discuss endlessly because the artistic value of pictures just cannot be decided in this way. Neither can
the question of whether a law is known be decided by measuring the evidence for it against any
standard, for it is not in the nature of evidence that the criterion of knowledge lies.
Whether or not it is possible for us to know about the minds of others, the past, or the future,
does not depend upon our evidence, we might be blind and deaf and yet know about them: it depends
only upon the possibility of our having the ability to make correct judgments about these various sorts
of fact. Stuart Hampshire6 points out that however right or wrong we may be about the minds of others,
or however adequate or inadequate our evidence for our beliefs about them, yet we certainly know that
they are often correct in their assertions about our own experiences and thoughts. Surely this is
sufficient warrant for me to assert that some other people have knowledge of at least one other mind,
my own. It would not be correct to say that their judgments, though correct, were merely accidental.
My assertion that others have knowledge of my mind is not based upon any estimate of the strength of
their evidence but only upon my evidence of their ability to make correct judgments about what I am
thinking.
Therefore discussions of whether the evidence for the hypotheses upon which we base our
assertions is good evidence, and discussions of whether these hypotheses are significant, are irrelevant
5
6
J. Thomson, Mind, July 1951.
Mimd, January, 1952.
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to the question whether we have knowledge of the minds of others. For we might have the ability to
make correct judgements about the minds of others without employing any hypotheses.
Of course there are situations in which it is impossible that a person should have a certain kind
of knowledge, but this is always for factual reasons. The information clerk who answered a traveller
with “How do you expect me to know anything, cooped up in this box all day?” was referring to such a
physical limitation. But it is never possible to be logically certain that a person deprived of the usual
evidence for some sort of fact will not know that fact: if it were then how could new kinds of evidence
come to be accepted?
What I have said has no bearing on whether people do make correct assertions about the
minds of other people, or on whether they ever have the ability to judge what other people are feeling or
would be feeling in certain circum stances. All that I have argued is that, if they do have this ability, for
which their being correct about the feelings of others would form strong evidence, then they do know
about the feelings of others. We may discuss whether people have the ability to judge the feelings of
others, but, if we decide this question, then there is no further question of whether they know about the
feelings of others.
It follows in a parallel fashion that the fact that the evidence upon which I base my judgments
about the properties of physical objects does not entail my judgments about physical objects does not
entail that I can never know these judgments to be true and hence does not entail that I can never make
these judgments. And again that the fact that it is always logically possible that I should believe what is
not true does not entail that I cannot ever know any propositions at all. For I may in fact sometimes
have the ability to accept true propositions and reject false ones.
Having knowledge depends neither upon an a priori justification, as the Rationalists supposed,
nor upon a justification by experience, as the Empiricists supposed.
The Second Argument
The second sceptical argument is more difficult to refute because it does not in the first place
try to prove so much. It attempts to establish that we cannot ever have direct knowledge of the events of
the minds of others, of the events of the past, of the properties of physical objects, and only from this
does it go on to argue that we cannot speak meaningfully about these matters and hence cannot have
knowledge of them at all.
The first argument went: since we cannot know about these matters we cannot speak
meaningfully about them. The second argument goes: since we cannot have direct knowledge about
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these matters we cannot speak meaningfully about them.7 Or, since we cannot verify any statements
about these matters we cannot make any statements.
I will set out the argument using as an example the attempt to prove that we cannot talk
meaningfully about physical objects which are independent of our minds.
Suppose, for the sake of the argument, that we can and do express propositions about physical
objects independent of our minds. Then all our knowledge about these objects will be obtained from
our knowledge of our sensations: the judgments we make about physical objects will be based upon
judgments about our sensations. Of course the judgments about physical objects will not be consciously
inferred from judgments about sense-data. As a matter of fact all our judgments about physical objects
are the result of these conscious or unconscious inferences and it is not easy to conceive how we could
have knowledge of physical objects which was not obtained in this way. Therefore the only way we
have, or can envisage, of deciding propositions about physical objects is by judgments about sensations.
Therefore propositions about physical objects are about sensations and there are no propositions about
physical objects independent of our minds.
Arguments similar to this have been used by philosophers to establish a great many different
conclusions: for example, to establish that statements about what is now the past are statements about
the present, that statements about what would happen if something which did not happen had
happened are statements about what has happened or will happen, that statements about the time at
which the universe began are meaningless, that statements about the position of an object in space are
statements about its relations to other objects, that to say that a mathematical proposition is true means
that it can be derived from the axiom system to which it belongs, that to say that an empirical statement
is true is to say that all the evidence is in favour of it, that when Smith says that Jones is in pain he
means something different from what Jones means when he says that Jones is in pain, and that it does
not make sense to talk of the shape of the mountains on the other side of the moon. Many philosophers
accept some of these arguments, few would accept them all, but the selections they make are different.
Many would accept the argument to the conclusion that statements about an object’s spatial position
are statements about its relations to other objects, very few would accept the argument to the
conclusion that it does not make sense to talk of the shape of the mountains on the other side of the
moon. Opinions differ about the status of the argument as applied to contrary-to-fact conditionals, to
statements about the past, about the minds of others, and about the properties of physical objects.
7
It is sometimes said that there are two problems about other minds: an inductive problem and a
problem about meaning. I think that what is meant by this remark is that there are two problems about
knowledge of other minds, both of which lead to problems about meaning: one a problem about how
we can know about other minds, the other a problem about how we can know directly about other
minds.
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According to which of the arguments a philosopher accepts and which he rejects, so his account of the
mistakes that may be made in the argument varies.
The form of these arguments is made explicit by the Verification Principle. The principle
states that nothing is meaningful to a person unless he can verify it and that the meaning of anything is
given by the method of verification. To investigate the force of this argument we must first discover in
what way verifying a proposition is different from just finding out whether it is true or false. To verify a
proposition is to find out whether it is true or false but to do so by a method which is superior to all
other methods of testing the proposition, a method to the results of which all results obtained by other
methods must give way, a method, therefore, which is logically certain to give the correct answer. “This
result was obtained by the verification procedure” entails “This result is correct”. The Verification
Principle holds that there is such a method for every proposition, or rather it holds the more
complicated thesis that all propositions arc logically related in a specified manner to propositions for
which there is such a method. Since this refinement is not relevant to my argument I shall not discuss it
or refer to it again. The principle is used in my example of the argument. For there it is argued that
either the best way of deciding propositions about physical objects is by deciding propositions about
sensations or there is no best way of deciding propositions about physical objects.
The assertion that the meaning of a proposition is given by its method of verification is more
difficult to explain. It means, according to what I have just said, that the meaning of a proposition is
given by that method of testing after the performance of which an unquestionable assertion may be
made. Since I shall not argue from any statement of this principle I do not need to discuss it more fully.
The principle is sometimes expressed by saying that the meaning of a proposition for me is given by the
best possible evidence which I can have for it. But this is either trivial or false. It is trivial if it means
“best possible that I could have”, for this evidence would be the proposition itself. It is false if it means
“best possible that I can physically have”, for this evidence might only factually imply the proposition.
It is clear how this argument is used in my example of the argument as applied to physical
objects: for a step is made from “the best way of deciding propositions about physical objects that can
be envisaged is by deciding propositions about sensations” to “propositions about physical objects are
about sensations”.
Criticisms of the Argument
I have already said that no one accepts the application of the argument in which it is used to
establish that we cannot talk about the shape of the mountains on the far side of the moon. And the
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reason that has generally been found for rejecting it is that it involves the view that a sentence is
meaningless if there is no method by which it can in fact be verified. This, it is said, is not true. What is
true is that a sentence is meaningless if there is no conceivable means of verifying it. And this in its turn
is sometimes explained as meaning “if there is no logically possible means of verifying it “.
A. J. Ayer has used this same criticism against the argument as used against statements about
the past8 and statements about other minds.9 I have myself criticized in this way the argument as used
against contrary-to-fact conditionals.10 Ayer argues that a statement about the past does not state that it
is a statement about the past, therefore it is not logically impossible that he should now be verifying it.
He could be verifying propositions about the battle of Waterloo if it were going on now and if he were
in the battle. He argues that it is logically possible that he should verify statements about the mind of
another because it is logically possible that he should be another. I argue that it is not logically
impossible to verify conditionals whose antecedent is not fulfilled because it is logically possible that the
antecedent should have been fulfilled. Now although the arguments about the past and about contraryto-fact conditionals are sound, the argument about other minds is not, for it is not possible for me to be
someone else and to remain myself.11 M. Shearn12 maintains that the argument about the past is not
sound either, for, very briefly, what sense does it make to say that the Battle of Waterloo might be
occurring now?
Therefore either there are invalid applications of the verification principle argument even
when only the logical possibility of verification is required for meaning, or my statement that you are in
pain means something quite different from your statement that you are in pain.
The fault with the argument is a much more fundamental one. It is present in the argument
which proves we cannot talk of physical objects that are independent of our minds as well as in the
argument that we cannot talk of the feelings of others but only about their behaviour.
It is the mistake of supposing that propositions have verification situations, that for every
proposition, or for every proposition of a very important kind, there is a privileged person, or a
privileged method of investigating, or a privileged position in which a person can stand, such that being
this person, or having carried out the method of investigating, or having attained the position, allows an
unquestionable and therefore true assertion to be made.
I shall first show that this is a mistake and then go on to show how avoiding it removes the difficulties.
A verifiable proposition is one for which the fact that it is true entails the fact that anyone who has
8
Philosophical Essays
Ibid.
10
Fact and Theory thesis in University of London.
11
Ayer on Other Minds, J. Watling, Theoria, 1954.
12
In a forthcoming paper.
9
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carried out the verification method believes it to be true and for which the fact that anyone who has
carried out the verification method believes it to be true entails that it is true. Therefore what any
verifiable proposition states is that if anyone has carried out a prescribed investigation, then he will
believe the proposition. Believe what? Believe that if anyone has carried out the prescribed
investigation, then he will believe the proposition. Believe what? And so on. The proposition that Jones
believes p, where p is the proposition that Jones believes p, is not a proposition at all. For a full
discussion of this point I must refer to G. Ryle’s article on the concept “heterological”.13 Therefore a
proposition which was verifiable would not be a proposition at all.
I believe that this argument is crucial, but there are other paradoxes to which the position gives rise.
The sort of knowledge which we have of a proposition when we verify it, when we know it directly, is
considered to be logically superior to the knowledge that we have of it when we are not verifying it. So
different that unless we can have this sort of knowledge of a proposition, then it is not meaningful to us
at all. But it is necessary and sufficient for this sort of direct knowledge that we should be in a particular
situation. Therefore to say that a person has direct knowledge of a verifiable proposition is to say no
more and no less than that he is in a particular situation. And the same is true of the statement that a
person believes a verifiable proposition through verifying it. Now is not this an extremely paradoxical
thing to suppose? How can believing any proposition be the same as being in a certain situation or
having performed a certain procedure? To suppose this would be like calling a man an artist because he
was born with a caul. As I argued in the first part of this paper, knowing that something is the case is
having an ability, the ability to tell the truth about that matter, how can being in a particular situation
or having carried out a prescribed method be identical with having an ability, any more than having the
ability to paint pictures can be identical with being born with a caul?
Therefore the view that some propositions are verifiable, if it is not contradictory, leads to
these two paradoxes: That all statements are statements about the conditions under which somebody is
said to know something and that statements that someone has direct knowledge and direct belief state
that he is in a certain situation or has carried out a certain investigation.
It is sometimes suggested that propositions about how things seem are verifiable propositions,
and that the person who asserts them cannot be mistaken about them. Evidently this arises from a
confusion between two quite different meanings of “seems”. I can say “This seems to me to be a lion”
meaning “I think that this is a lion” and since the assertion of this statement demonstrates that I do
think that this is a lion, then I cannot very well be mistaken when I make it. But I might also say “This
13
Analysis, Volume II, No. 3.
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seems to me to be a wolf but I think it is a lion” and in this sense of “seems”, where it means “looks like”
I might very well be mistaken. “No, it doesn’t look like a wolf to you”, my friend might reply “doesn’t its
tail curl up and not down?” Or he might show me a picture and I might agree that that was what I saw
and then he might ask how I could possibly have said that that looked like a wolf and I might agree that
I was wrong.
The most hopeful candidates for verifiable propositions are propositions about sensations, for
these may in fact be tested better by the person who is having the sensations at the time at which he is
having them than by any other person or at any other time. Of course the same logical difficulties arise
if it is supposed that the fact that I am having a sensation is identical with the fact that I believe that I
am having a sensation. Again I think that the belief that having a sensation is knowing that you have it
arises from not seeing clearly that to know something is to have the ability to state it. It does seem
impossible to have a visual sensation and not to know what it is like because we confuse having the
sensation with knowing that we have it.14 If to remove this confusion, we imagine a test of whether we
know what a certain sensation is like, a test in which another sensation is presented and we are asked to
say whether it is the same as the sensation in question, then it is not so obvious that we know what our
sensations are. Is it obvious that a sensation of a complicated and unfamiliar kind could be recognized
again without mistake, or that two groups of sensations occurring simultaneously could be recognized
as similar without the possibility of error?
People have wanted to hold that each proposition, or each of some very important kind of
propositions, has a verification situation because they have supposed that unless there were some
situations in which they were logically bound to be correct, then they might be mistaken no matter
what precautions they took, no matter what evidence they piled up; piling up evidence would be
irrelevant because it would bring them no nearer to certainty. But how could it ever be logically
impossible for something to be true and for me to believe it false? The fact would have to be both the
fact we believed and the fact that we believed it. Is it conceivable that any important empirical
propositions should be of this kind? Anyway the statement that every proposition has a privileged
verification situation does not entail that there are facts about which it is logically impossible for us to
be mistaken. All that ‘the cat is on the mat’ is verifiable entails is that there is a privileged situation such
that if I am in that situation, then I know whether the cat is on the mat. The problem of whether I am in
the privileged situation remains.
14
G. E. Moore in Some Main Problems of Philosophy: “What Russell calls knowledge by acquaintance
is not knowledge at all (nor acquaintance either for that matter)”.
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If the above argument is correct, then there is not any proposition which has a method of
testing it which is logically superior to all other methods of testing it, there is not any proposition which
has a person or a situation, such that the opinion of anyone who is this person or who is in this
situation must take priority over the opinion of anyone else. The question “What do I know?” is
logically distinct from the question “What methods of investigation have I carried out?” though, of
course, factually dependent upon it. The question “Do I have the best possible evidence for this
proposition?” is logically distinct from the questions “Am I a certain person? Am I in a certain
situation?” To have evidence is not to have the right to speak, but to have the ability to speak truly. This
is not an ability that can be granted to you by the other users of your language just as being able to paint
pictures is not an ability that can be granted to you by people who are willing to pay large sums for your
paintings. Once this is realized, then a great deal of sceptical doubt disappears.
It follows, first, that my knowledge of the events of your mind is not of a logically inferior kind
from your knowledge of them, though mine is by inference and yours is not. Though you have your
pain and I do not, you do not know that you have your pain any more than I do. Having a pain is not
identical with having evidence that you have a pain. Pieces of evidence are facts, not things which are
not facts. It is often argued that Jones has evidence for Jones being in pain that Smith could not have:
Jones has the pain and Smith could not have it. But if Smith knows that Jones is in pain, then both
Smith and Jones have the evidence that Jones is in pain. Smith has just the same evidence as Jones
though, of course, Smith inferred this piece of evidence from other facts, about Jones’ behaviour, and
Jones did not. The only distinction is between knowing by inference and knowing without inference.
The problem of how can we check our inferences from a man’s behaviour to his sensations is easily
solved: for to check such an inference it is necessary to know how be behaves on a particular occasion
and to know what his sensations are, it is not necessary to know how he behaves and to have his
sensations; any other reliable method of knowing whether he has sensations will do to check our
inferences. When we check our knowledge all we can ever do is to check one way of finding something
out against another way of finding it out: there is no way of checking the result of a test against the fact
itself no way of getting so close to a fact that your statement about it just cannot be wrong. Of course if
you have no reliable method to check against, then you cannot check your knowledge. It may be that we
have no reliable method of finding out about the minds of others: there are a great many matters about
which we have no reliable method of finding out: I am only arguing that there is no logical bar to
having knowledge of other minds, not that we have such knowledge.
Exactly similar considerations apply to the argument that we cannot have direct knowledge of
the properties of physical objects which are independent of our minds. The argument depends on the
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step from “all my judgments about physical objects are based upon judgments about sensations” to “I
have direct knowledge of my sensations of a sort which I cannot envisage having of physical objects”.
The demand is made that it must be conceivable that I should have direct knowledge of physical objects
if I am to talk meaningfully about them. But this knowledge, which it is demanded that I must have of
physical objects, I do not have even of my sensations, nor could I have it of anything. It is logically
possible that I should have non-inferential knowledge of physical objects, just as I have non-inferential
knowledge of the past by memory, and might have non-inferential knowledge of the minds of others by
clairvoyance, but this is not direct knowledge of the privileged kind that I have been thought to have of
my own sensations.
This, then, is the mistake made in many applications of the Verification Principle argument:
the mistake of demanding that every proposition has a verification method. But not all applications of
the argument involve this mistake. For example the argument that statements about spatial position are
statements about relations to physical objects. This argument only involves the assumption that there
must be some conceivable way of testing a statement, it does not involve that there must be a best way,
and this more modest statement of the verification principle seems to me to be true.
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