MORE ON SCIENTIFIC EXPLANATION
For van Fraassen all explanation is a
“pragmatic” activity.
What he means by this:
 An explanation is an answer to a “why”
question.
 The correct answer to these questions
will depend on the context, including the
interests of the questioners.
Let’s see why.
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An example
Suppose a person, S, dies. We ask for an
explanation of this.
Consider various possible replies:
 Observer: he was in a car accident
 Doctor: massive hemorrhaging of the
brain tissue.
 Lawyer: negligence on the part of the
other driver.
 Engineer: brake construction prevented
the car from coming to a timely stop.
 City planner: a poorly placed tree, which
blocked the view of oncoming traffic.
All of these pick out something that is
relevant to the event, but can we say which
one is the explanation of the death?
Van Fraassen: No!
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Context dependence
According to van Fraassen, the context of
inquiry determines which hypothesis is
relevant. E.g.:
 In the context of a legal proceeding, we
are only interested in hypotheses that
bear on legal accountability.
 In the context of medical reports, we are
interested in physiological hypotheses.
 In the context of an inquest into the
safety of public roads, we are interested
in objects that might obscure a driver’s
vision.
 Etc.
In other words, relevance is contextdependent and this is a general feature of
explanation.
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Asking questions
Notice that each explanation is an attempt
to answer the question: “Why did S die?”
 The answer took the form of a
proposition: a claim that describes a
relevant event or situation.
So, perhaps we can sum up van Fraassen’s
theory as:
Explanation is an answer to a why question
whose relevance is determined by context.
Not quite.
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Determining questions
Consider this question:
 Why did Adam eat the Apple?
This can be construed in different ways:
1.
2.
3.
Why was it Adam who ate the
Apple?
Why was it an Apple that Adam ate?
Why did Adam eat the Apple?
How can one phrase give rise to so many
questions?
 Van Fraassen: because every question
is implicitly a comparison.
Let’s see what he has in mind:
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The form of questions
Van Fraassen: it is a mistake to think that
when we ask a question we are simply
asking:
 Why (is it the case that) X?
Rather, we are asking:
 Why (is it the case that) X (rather than
Y)?
In other words, a question always has a
contrast class.
 A contrast class is a set of alternative
answers to a question.
 Which alternatives are relevant is
determined by the context.
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Adam and the apple
So, the question “Why did Adam eat the
Apple” has different answers depending on
whether:
1a. We want to know why Adam in
contrast to other people at the apple.
2a. We want to know why Adam ate the
apple in contrast to other pieces of
food.
3a. We want to know why Adam ate the
apple rather than threw it out.
In 1a, the contrast class is other people. In
2a it is other food. In 3a it is other actions.
The contrast class is determined by context.
 You can normally find out by examining
the situation and the questioner which
class she or he is interested in.
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More on contrast class
Consider:
 Why did S (who smokes) get lung
cancer (as opposed to staying healthy)?
Consider two cases:
1. This question is asked by S’s mother
during a social occasion.
2. This question is asked by S’s mother
during a discussion of smokers.
If the context is given by 1, then a good
answer is: because S smoked.
If the context is given by 2, then the same
answer is no good—we are still left
wondering.
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Making something stand out
In other words, in giving an explanation, one
must provide an answer that explains why S
stands out from his/her contrast class.
 If the contrast class is the general
population, then S’s smoking does make
him/her stand out.
 If the contrast class is other smokers,
then S’s smoking does not make
him/her stand out.
Making something stand out in this way
satisfies the questioner.
 It eases her/his sense of wonder.
 This makes the answer an explanation.
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Summary of the view
So, in providing an explanation of X we
must answer the question “Why X” with a
proposition, P, that is:
 True
 Relevant (determined by context)
 Makes it more probable that X than any
of the other alternatives in the contrast
class.
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Scientific explanation?
So, when is an explanation scientific?
There is no such thing as uniquely scientific
explanation for van Fraassen.
Sometimes, however, the context
determines that we need scientific theories
to help determine relevance, contrast class,
etc.
 Here science enters into the process of
explanation.
Also, in a given context, the answer to a
question might be a proposition from
physics, chemistry, biology, etc.
 We may call it a scientific explanation.
Explanation is, ultimately, a matter of the
logic of pragmatics, not the content of
scientific theories.
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Contrasts
As opposed to Hempel, van Fraassen
believes there is no fundamental difference
between explanation and description.
 For him, an explanation just is a
description with certain relevant
properties.
Also, van Fraassen thinks there is no single,
absolute theory of explanation:
 The appropriate explanation is
determined by context.
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More contrast
Van Fraassen’s view differs from Salmon’s
as well.
Salmon thinks we have explained why X
occurred when we find the cause of X.
 But as the car accident example shows,
van Fraassen thinks there is no single
answer as to what causes something.
 The correct answer to a causal question
depends on the context.
Also, Salmon’s view can’t handle
indeterministic theories, such as QM.
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Indeterminism and causation
For Salmon, if A & B are statistically
correlated but neither causes the other, then
we have explained them when we cite a
common cause:
 Pr(A & B/C) = Pr(A) x Pr(B)
 Pr(A/B & C) = Pr(A/C) (C screens of B
from A)
But suppose C is invariably followed by
either A, B or D with equal probability:
Pr(A/C) = Pr(B/C) = Pr(D/C) = 1/3
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The counter-example
Let A v D = P and B v D = Q
Pr(P/C) = 2/3 (A and D are 2 of 3 options)
Pr(P/Q) = ½ (B and D are equally
probable; one of them entails
A v D but not the other, so
50-50)
Pr(P/C&Q) = ½
(given C and B v D, then
either D occurs or B
occurs, with equal
probability; the former
entails P, the latter does
not, so 50-50).
So, Pr(P/C&Q)  Pr(P/C), and C does not
screen of Q from P.
So, C is not an explanation of P and in
general indeterministic correlations will
never count as explainable.
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Asymmetry
Note: since context determines relevance, it
determines what counts as a good answer
to a question.
 So it will determine whether A explains
B or B explains A.
If, in a context, C, only one of those holds,
then the asymmetry of explanation arises.
Probabilistic accounts can’t explain this:
E.g. Pr(barometer rises/atmospheric
pressure drops) = Pr(atmospheric pressure
drops/barometer rises)
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Kitcher on explanation
Kitcher: Let K = a set of sentences (beliefs,
claims, propositions) that are accepted as
true.
 E.g.: K might be observations of
planetary motion, spectral patterns of
heated elements, behaviour of animals,
etc.
The question is:
 Which arguments count as a good
explanation of K?
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Deductions
Kitcher: we want arguments that allow us to
deduce the members of K from other
statements we accept (including laws).
 This is because science is about more
than just listing facts.
We want to systematize K so that we
understand it.
But there are different ways we might
systematize K.
 Which ones provide explanations?
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Unity
Kitcher: our goal is to unify K:
 Minimize the kinds of arguments
(derivations) needed, and
 Maximize the number conclusions
(members of K) that we can derive.
In short, we want to find one (or a few)
patterns of argument that allow us to derive
as many members of K as possible.
An argument that is an instance of such a
pattern, counts as an explanation of K.
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History of science
Kitcher: the history of science supports my
view. Consider successful theories, such as
Newton’s or Darwin’s.
 We see that they are often accepted
well before they’ve made a lot of
successful predictions or been
empirically verified to a very large
extent.
Why is this? Because:
 They provide patterns of argument that
allow us to derive a large number of
claims which we accept as true from a
small number of assumptions.
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Example: Darwinian evolution
Darwin proposed that biological features of
an organism are the result of:




Features of its ancestors
Nature of their environment
Laws of variation and inheritance
Natural selection
Kitcher: Even though the laws of genetics
weren’t known at the time, Darwin’s theory
was widely accepted.
 This is because it became clear that
pretty much any observed biological
feature could be derived by an argument
patterned on the one above.
E.g.: size, colour, fur, appendages, etc.
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Against Hempel
Hempel’s account has an asymmetry
problem:
 We can derive the length of a pendulum
from its period (and laws of motion) or
vice versa.
However, the length of the pendulum
explains why it has the period it does; its
period does not explain why it has the
length it does.
 Hempel’s view can’t say why this is so.
Kitcher: my account can…
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An example of unification
Kitcher: Suppose we decide to derive the
length of the pendulum from its period.
 If so, we need a different pattern to
explain why motionless pendulums have
the length they do.
 Either that, or refrain from explaining it.
On the other hand, if we derive the length
from facts about how the pendulum was
formed, then we have a pattern that works
for all objects.
 This pattern is more unifying, so it
counts as the correct explanation.
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Another example
Here is a Hempel-style explanation:
All blessed salt dissolves in water
This salt has been blessed.
Therefore, this salt dissolves in water.
This is no explanation, but how can Hempel
rule it out?
Kitcher: He can’t, but I can.
 If we count this as an explanation, we
need a different kind of explanation for
non-blessed salt, which also dissolves.
 But, if we stick to chemical theory, we
have one pattern of argument for all salt.
 Since this is more unifying, it counts as
the better explanation.
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In sum
Kitcher argues that his theory avoids
problems that plague Hempel’s.
Also:
 It shows that there are general features
of explanation that go beyond pragmatic
concerns (against van Fraassen).
 It allows for non-causal explanations
(against Salmon).
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