94 The Debate over the Consequence Argument
deny that to be able to do something is to be able to add to the given past. More
precisely, the compatibilist backtracker will deny the following principle:
For all S, t, bt, and at, if Ost at then Ost (bt&at).To this denial Ginet objects that we seem to use this principle in making infer-
ences of which we are confident. For example:
Push- ups: Given the premises that I have done 20 push- ups in the last five
minutes and that it is now open to me to do four push- ups in the next
minute, I will have done 24 push- ups in six minutes.The compatibilist backtracker must say that rather than using the principle of the
fixity of the given past in such inferences, we use instead:
For all S, t, bt, and at, if Ost at & X, then Ost (bt&at).The X in inferences like push- ups will be:
(1) If it had been the case that at, then it would (still) have been the case
that bt.In some other possible cases, the true conditional, by contrast with (1), is
instead:
BT: If it had been the case that at, then it would have been the case that
not- bt.In such cases, it is not open to the agent to add to the given past, and the possib-
ility of such cases makes it the case that the principle of the fixity of the given
past is false. The backtracking compatibilist needs to say that in push- ups we
would need to assume a principle of the form of (1), that if S had done four
push- ups in the minute after t, then it would still have been the case that S did 20
push- ups in the five minutes before t.
In Ginet’s opinion, the compatibilist backtracker must agree that this account
is highly implausible, for in the sort of case at issue, it’s implausible to suppose
that this sort of backtracking counterfactual is true. Suppose that in push- ups, I
don’t actually do four push- ups in the next minute—I don’t do any. We would
then need to be confident that in the nearest possible world in which S does four
push- ups in the minute after t and the laws of nature are exactly the same as they
are in the actual world, it would be true that S did 20 push- ups before t, and thus
24 within six minutes, and no more or less. Ginet argues that it would be difficult
on the backtracking view to be confident of this claim, for the reason that any
minimal set of changes in the past needed to allow it to be true that S does four
push- ups in the minute after t is likely to ramify vastly into the past, in particular