Theism and Explanation - Appeared-to-Blogly

Inference to the Best Explanation 111
proposed explanation on offer is a bad one, it would be better to admit
that we have no (satisfactory) explanation at all. 47
What if the proposed theistic explanation were the only possible explanation
of some fact? What if the fact in question were naturally inexplicable,
not merely (contingently) unexplained? In these circumstances, would the
proposed theistic explanation not win by default, even if it did not appear
to be a very good explanation? Well, we would fi rst have to be satisfi ed that
the fact in question had an explanation, that is to say, “a suffi cient reason
why it is thus and not otherwise.” 48 For it may turn out to be a “brute fact,”
one lacking an explanation (4.3.2.2) and it would be better to accept this
than adopt what would be an unsatisfactory explanation. And how could
we know that the proposed theistic explanation was the only possible (not
merely the only available) explanation of the fact in question? We are rarely,
if ever, in this situation. And if we cannot be certain there is no alternative,
and the proposed theistic explanation was less than satisfactory, we would
always be justifi ed in seeking an alternative.
If this line of argument is correct, then I can further refi ne Peirce’s
schema, by rewording premises (2) and (4).
(1) The surprising fact, E, is observed.
(2) H would be a satisfactory explanation of E.
(3) No available competing hypothesis would E as well as H does.
(4) It is reasonable to accept the best available potential explanation of
any fact, provided that explanation is a satisfactory one.
(5) Therefore it is reasonable to accept H.
But this merely brings me back to my initial question: By what criteria do
we judge H to be the best explanation—or a satisfactory explanation—of
E? Given that H is a potential explanation of E, what other features should
it possess to make it worthy of our acceptance?
It is tempting at this point to offer a “justifi cationist” answer to this
question (2.1.3.1), similar to that favoured by Swinburne, with his appeal
to confi rmation theory. If a true explanation is what we want, then surely
the “best” explanation is simply that which is most probably true. So we
would be justifi ed in accepting a potential explanation H if
Pr(H|E & K) > 0.5
and there exists no competing hypothesis whose probability given E and K
is higher. If we adopt this solution, we can use Bayes’s theorem to take us
from the likelihood of E given H to the probability of H given E and K.
But as I argued earlier (2.1.3.2), this sets too high a standard. There are
many instances of people accepting scientifi c theories even though their
posterior probability has not yet been shown to be greater than 0.5. And