2 0 0c hAp tEr 9 ■ I n f e r e n c e t o t h e B e s t E x p l a n a t i o n a n d f r o m A n a l o g ystrong reasons to believe that cats cannot break metal locks. This rules out
the hypothesis that your neighbor’s cat broke your front-door lock. Explana-
tions should also not contain claims that are themselves too unlikely to be
true. A meteorite would be strong enough to break your lock, but it is very
unlikely that a meteorite struck your lock. That makes the burglary hypothe-
sis better, at least until we find other evidence (such as meteorite fragments)
that cannot be explained except by a meteorite.
In sum, a hypothesis provides the best explanation when it is more ex-
planatory, broad, powerful, falsifiable, modest, simple, and conservative
than any competing hypothesis. Each of these standards can be met to vary-
ing degrees, and they can conflict. As we saw, the desire for simplicity might
have to be sacrificed to gain a more powerful explanation. Conservatism
also might have to give way to explain some unexpected observations, and
so on. These standards are not always easy to apply, but they can often be
used to determine which explanation is best.
Once we determine that one explanation is the best, we still cannot yet
infer that it is true. It might turn out that the best explanation out of a group
of weak explanations isn’t good enough. For centuries people were baffled
by the floods that occurred in the Nile river each spring. The Nile, as far as
anyone knew, flowed from an endless desert. Where, then, did the flood wa-
ters come from? Various wild explanations were suggested—mostly about
deities of one kind or another—but none was any good. Looking for the best
explanation among these weak explanations would be a waste of time. It
was only after it was discovered that central Africa contains a high moun-
tain range covered with snow in the winter that a reasonable explanation
became possible. That, in fact, settled the matter. So it must be understood
that the best explanation must also be a good enough explanation.
Even when an explanation is both good and best, what it explains might be
illusory. Many people believe that shark cartilage prevents cancer, because the
best explanation of why sharks do not get cancer lies in their cartilage. One
serious problem for this inference is that sharks do get cancer. They even get
cancer in their cartilage. So this inference to the best explanation fails.
When a particular explanation is both good and much better than any
competitor, and when the explained observation is accurate, then an infer-
ence to the best explanation will provide strong inductive support. At other
times, no clear winner or even reasonable contender emerges. In such cases,
an inference to the best explanation will be correspondingly weak.Context Is Crucial
Whether an inference to the best explanation is strong enough depends on
the context. As contexts shift, standards of rigor can change. Evidence that is
strong enough to justify my belief that my spouse took our car might not be
strong enough to convict our neighbor of stealing our car. Good judgment is
often required to determine whether a certain degree of strength is adequate
for the purposes at hand.97364_ch09_ptg01_195-214.indd 200 15/11/13 10:47 AM
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