Theism and Explanation - Appeared-to-Blogly

Inference to the Best Explanation 109
(1) The surprising fact, E, is observed.
(2) But if H were true, E would be a matter of course.
(3) Therefore H is true.
Such an argument would embody a well-known logical fallacy, namely that
of affi rming the consequent. 38 It is a fallacy of the The streets are wet; if
it has been raining, the streets would be wet; therefore it has been raining
variety. In symbols, the argument involved would have the following,
invalid form.
P ⊃ Q
Q
∴ P
If this is how we justify our belief in unobservables, then A. J. Ayer was
surely right: the inference involved is illegitimate. 39
Let me illustrate the diffi culty. I suggested earlier (3.1) that the discovery
of electrons was a scientifi c discovery backed up by abductive reasoning.
One of the factors that led to the discovery of electrons was the attempt
to explain the behaviour of cathode rays. In particular, J. J. Thomson
suggested that the behaviour of cathode rays could be understood if we
assume that they “mark the paths of particles of matter charged with negative
electricity.” 40 But the danger with such reasoning is that there are other
ways in which cathode rays could be explained. In fact, in Thomson’s day
there was a competing hypothesis, namely that of “some process in the
aether.” 41 I shall refl ect later on how Thomson chose between these competing
hypotheses, in order to argue that the electron hypothesis was the better
explanation (7.1). For the moment, I want to note merely that the electron
hypothesis was not the only potential explanation of the data. And even
if it were, Thomson could not have excluded the possibility that another,
preferable explanation existed.
The general principle should be clear. The mere fact that some hypothesis
would explain the data, if it were true, does not entail that it is true. As
Alan Musgrave writes, “any sane philosopher can think of countless cases
where an explanation of some surprising fact is false. It is a surprising fact
that fossils are found on mountain tops. One explanation is that Martians
came and put them there to surprise us. But this explanation is not true.” 42
What makes us think the Martian hypothesis is not true? It is the fact
that we have a better explanation. So perhaps we can reformulate Peirce’s
abductive schema as a form of inference to the best explanation (IBE).
(1) The surprising fact, E, is observed.
(2) If H were true, E would be a matter of course.
(3) No available competing hypothesis would explain E as well as H does.
(4) Therefore H is true.