Phil 148
Inferences to the Best Explanation.
• IBE is also known as ‘abductive reasoning’
• It is the kind of reasoning (not deduction) that
Sherlock Holmes is really famous for.
• A hypothesis gains support if it accords with
our background beliefs and works better than
any competing explanation.
• On the next slide is a set of standards by
which we evaluate IBEs. Many of these
standards will be reused on other aspects of
inductive reasoning.
The “Hat Trick”
• Witness a television adaptation of a part of
the Arthur Conan Doyle story “The Blue
• http://www.youtube.com/watch?v=1bCS4icTr
Standards for IBE (or any explanation for
that matter)
A good IBE:
…makes sense of what it seeks to explain.
…is deep, that is, the explanation itself does not need further
…is powerful, that is, the explanation could be used over a
wide range of cases.
…is falsifiable, that is, the explanation can be wrong.
Explanations that can’t be wrong in principle are vacuous.
…is modest, or does not claim any more than it has to.
…is simpler than competing explanations with equal
explanatory force.
…is conservative, that is, forces us to revise or give up as few
of our previously held beliefs as possible.
• First off, any explanation must be consistent
with what it seeks to explain. It should fit all
of the relevant evidence.
Depth of Explanation
• An explanation is shallow to the extent that it
itself requires explanation.
• Book: “Why did the police raid your house?”
Because they suspected you.
Power of Explanations
• An explanation is powerful to the extent that it
explains more than just a few special cases.
• Einstein’s theories replaced Newton’s theories
because they could explain a wider range of
• Be careful though, when a theory (like the
indefinite discrete ghosts theory) explains too
much, because in so doing, it fails to explain why
the observations came out the way they did as
opposed to any other way.
Falsifiability of Explanations
• A theory is falsifiable if it is subject to
disconfirmation by evidence.
• Non-falsifiable theories are sometimes called
“self-sealing”, e.g. “The reason you don’t believe
that aliens have taken over all life is that they
have gotten to your brain processes!”
• DO NOT confuse ‘falsifiable’ with ‘false’
• See Peter Woit’s “Not Even Wrong” for an
account of how string theory is not falsifiable
Modesty in Explanations
• An explanation or theory is modest if it does
not claim more than it needs to claim in order
to do the explaining.
• Occam’s razor, though often taken to be a
statement of simplicity in theory, is really a
statement of modesty. ("entities must not be
multiplied beyond necessity" (entia non sunt
multiplicanda praeter necessitatem))
Simplicity in Explanation
• Simplicity is something of a tie-breaker.
• There are many simple theories that fail other
criteria (like the indefinite discreet ghosts
• Simplicity is more of an aesthetic concern that
can apply when two theories explain the
phenomena equally well.
Conservatism in Explanation
• That we have believed a particular thing for a
long time is no reason to continue believing it,
so conservatism is never the most important
• However, we should not give up our best
theories lightly.
• An explanation is conservative to the extent
that it does not require the overturning of
existing and accepted theory.
Book Feature
• The Structure of
Scientific Revolutions,
by Thomas Kuhn
• Concerns just how and
why we hold onto
conservatism in
• A truly revolutionary
look at science
“Let the Facts Decide”
• Arguments involving underdetermination attempt to show that there is no
reason for belief regarding some theory because it is underdetermined by
the evidence. Since the evidence does not show that the theory is the
uniquely true hypothesis, there is no reason to believe it rather than some
equally supported rival.
• Because arguments involving underdetermination involve both a claim
about what the evidence is and that such evidence underdetermines a
theory, it is often useful to separate these two claims within the
underdetermination argument as follows:
– All the evidence of a certain type underdetermines which of several rival
theories is correct.
– Only evidence of that type is relevant to believing one of these theories.
– Therefore, there is no evidence for believing one among the rival theories.
• The first premise makes the claim that a theory is underdetermined. The
second says that rational decision (i.e. using available evidence) depends
upon evidence that underdetermines the theory.
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