Van Fraassen responds

There are many scientific theories about
things we can’t observe:
 Electrons, quarks, electric fields, strings,
This suggests a question: should we believe
unobservable entities exist?
 Those who believe we should are called
scientific realists.
 Those who believe we shouldn’t are
called scientific anti-realists.
Scientific realism is the belief that:
A. Scientific theories aim to give us a
literally true account of reality
B. Accepting a theory involves accepting
the theory as true
So, if you accept particle theory you accept,
e.g., that electrons exist.
Why might we doubt this?
Anti-realism: Positivism
Positivists claim that we can only
meaningfully talk about what is observable.
 So, when scientists talk about “quarks”
or “electrons” they mustn’t be
interpreted literally.
 What they are really talking about is
observations of instruments.
E.g.: “there is electric current in this circuit”
really means “the ammeter deflects when
connected to this circuit”.
So, positivism is a form of anti-realism by
arguing that theoretical claims shouldn’t be
taken literally.
Anti-realism: Constructive Empiricism
Van Fraassen disagrees. He thinks there is
no point in trying to re-interpret scientific
 So, scientific claims should be literally
But the aim of science is to give us theories
that are empirically adequate, not true!
Empirical Adequacy:
 Everything the theory says about what is
observable—e.g. meter deflections,
flashes of light, etc.—is true.
To accept a theory is simply to believe it is
empirically adequate.
Empirical adequacy
Van Fraassen: when choosing a theory, all
we ever have to go on is the observable
evidence in its favour.
If we claim empirically adequate
(successful) theories are also true then we
do two things:
 Make a claim that goes beyond the
evidence (truth is more than evidence);
this is a leap of faith.
 Accept that empirically adequate
theories might be false (again, truth is
more than evidence).
Both are undesirable. Instead we should
just accept those theories that work.
Pragmatic aspects
Van Fraassen: In adopting a theory we
shouldn’t believe it is true, but we do take
on a pragmatic commitment:
 To explain future phenomena using the
concepts, formulae, etc. of the current
 I.e., we intend to vindicate our theories.
There is no guarantee of success here:
 E.g.: funding to science might be cut
Still, for van Fraassen accepting a theory is
a matter of:
 Finding it to be empirically adequate
 Committing oneself to vindicating it
Observable vs. unobservable
Van Fraassen: since accepting a theory
only commits us to accepting as true what it
says about the observable realm:
 It follows that we don’t need to believe
any claims about the unobservable.
 We should remain anti-realists about the
But some have argued that there is no real
distinction between the observable and the
 If so, then van Fraassen’s position rests
on an untenable distinction.
Against the distinction
Argument I:
There are many ways in which we might be
able to detect some entity:
 Unaided eyeslow power magnifying
glasshigh power magnifying
glasslow power microscopehigh
power microscopeelectron
microscopecloud chamber.
This forms a continuum.
There is no principled place to draw the line
between observable and unobservable on
this continuum.
Therefore, there is no distinction between
the observable and unobservable.
Van Fraassen: Just because we don’t know
where to draw the line between observable
and unobservable it doesn’t follow that there
is no distinction.
 What follows is that it is vague.
E.g.: we can’t draw a definite line (in terms
of number of hairs) between being bald and
not being bald,
 Still the distinction exists.
All we need is clear cases on either side,
and we have that: what we can observe
without instruments vs. what requires
Against the distinction
Argument II:
What is observable by humans is a mere
accident of our evolution.
 We might have had senses so good that
we can, e.g., see quarks.
 We might evolve in the future so that our
senses become that good.
So, nothing is unobservable in principle.
Van Fraassen: This is not relevant.
 Is the CN tower portable because in
“principle” we could carry it?
 Is a steel girder fragile because in
“principle” we could break it?
 Of course not!
Since the aim of science is empirical
adequacy, we should only believe in what is
observable by our current abilities.
 Anything else is a leap of faith.
Realism strikes back
Van Fraassen’s arguments were influential,
in part because:
 It shares some features with positivism,
which was very influential.
 It avoids some of positivism’s more
controversial claims (i.e. re-interpreting
scientific language).
Nevertheless, realists responded…
The “Miracle” Argument
 Science is successful: our theories
make a lot of predictions that turn out to
be accurate.
 Such success couldn’t occur by mere
chance or guesswork.
 If our theories are false, then it would be
coincidence if any predictions derived
from them were true
 But if our theories are true, then any
conclusion logically deduced from them
must be true.
 Realism is the only explanation that
does not make the success of science
an extremely improbable miracle.
 Realism is the best account of science.
Van Fraassen responds
Suppose we were to ask why mice flee from
cats. How would we explain this?
Van Fraassen: We would appeal to Darwin.
In the past, there was natural variation in
mice: some ran, some didn’t.
 Those that ran survived and passed the
flee response on to their offspring.
 Those that didn’t died. Their traits died
with them.
In other words, some responses worked
and were propagated, some didn’t and were
Van Fraassen: there is no need to suppose
that some mice formed true theories about
cats while others didn’t.
The same holds for theories…
The Darwinian approach to science
Question: Why are theories successful?
Van Fraassen: There is variation among
theories: some are E.A., some aren’t.
 Those that are “survive”: scientists
adopt them.
 Those that aren’t, are rejected: they “die
It’s not that some theories “get reality right”
(truth) while others don’t. Rather:
 Anything that works has a survival
(acceptance) advantage.
We don’t need to explain why they survived
because there is no “miracle”:
 In a competitive environment,
successful strategies prevail.
Defending Realism
Brown: Science is successful means:
1. Our theories get a lot right: they unify,
organize and explain many things.
2. Science progresses: new theories get
more right than old theories.
3. Novel predictions are correctly made
more often than chance alone could
Can van Fraassen’s Darwinian approach to
scientific success account for all of these?
The Darwinian stance rests on an analogy:
 The success of theories is like the
survival of biological species.
 But does the analogy hold?
Novel predictions
Brown: When surprising or unexpected
phenomena occur, this is a radical change
in the environment of a theory.
 It is like a sudden alteration of a species’
 However, in nature, most species are
unable to survive radical change (e.g.,
But good theories only account for (survive)
novel observations, they predict them.
 So in one very important way, theories
are not like biological species
No explanation
What this shows is that van Fraassen’s
Darwinian approach can’t explain the
success of science:
 According to him, we accept theories
because they are empirically adequate:
they account for what we have observed
to date.
 But the fact that a theory is good at
organizing and unifying our past
experience gives us no reason to
believe it will continue to do so
 This is an induction problem.
What about points 1 & 2?
Brown: nor can van Fraassen explain the
first two aspects of scientific success. He
1. Our theories unify observations
because we pick the ones that do.
2. Our theories progress (unify more and
more) because we pick the most
successful ones available.
Brown: this is too simplistic: it assumes that
scientists only look at empirical adequacy
when choosing a theory. This is false.
 Other considerations can (and do) play
a role: conceptual, metaphysical, logical,
and even aesthetic.
 So there is more to rational acceptance
than empirical adequacy.
Some problems remain
 It is hard to come up with criteria for
“closer to the truth”—so, how do we
measure the progress of science?
 Even false theories make novel
predictions, so do these really show
theories to be true?
Let’s examine the last point:
 If false theories can make successful
predictions, truth isn’t necessary for
predictive success.
 Also, true theories can make false
predictions, so truth isn’t sufficient for
So does success really give us a reason to
believe theories are true?
Narrative explanations
Brown: some explanations are narrative:
 They are intended to show us how
something could be possible, not why it
is necessary (had to be).
E.g.: Giraffes have long necks because in
the past those with the longest necks had
the highest survival rate.
 We don’t know with certainty that the
past was like that.
 However, this story allows us to see
how a current situation could have
Brown: realism is like that!
 It is a story that allows us to see how
successful predictions are possible.
 That gives us some reason to believe it.