Thursday, June 24, 2010

The PSR, contrastive explanation and "rather than"

The Principle of Sufficient Reason (PSR) says that every contingently true proposition has an explanation. Suppose you are impressed by the following thought:

  1. In cases of libertarian free choice, while we can explain why x chose A by citing the non-necessitating reasons R for A, we cannot explain why x chose A rather than B by citing such reasons, since x would have had R even had x chosen B. In other words, there is no contrastive explanation for x's choosing A.
I think this is mistaken: there is a contrastive explanation, and it is given by the reasons. However, suppose that I can't convince you of this, and so I concede that one can't explain why x chose A rather than choosing B. Does it follow that the PSR is false?

On its face, it seems to. Let p be the "contrastive proposition" that x chose A rather than choosing B. If one can't explain why x chose A rather than choosing B, then one can't explain p. However, I have the following objection (developed with the help of various folks at the philosophy of religion summer seminar at the University of St Thomas). To demand an explanation of why x chose A rather than choosing B is not the same as simply to demand an explanation of any proposition. Instead, the "rather than" in "explain why x chose A rather than B" signals what sorts of explanations will be accepted for the conjunctive proposition that x chose A and x did not choose B—for instance, only those explanations that are contrastive in the sense that they would not hold if x chose B instead. So, on this response, in the contrastive demand for explanation, the proposition whose explanation is demanded has a perfectly good explanation, say in terms of the reasons for choosing A and the incompatibility between A and B, but the "rather than" phrasing contextually says that this sort of explanation is not going to be accepted (or, perhaps, modifies the meaning of "explanation" to "explanation of such-and-such sort"). And it is no counterexample to the PSR to observe that some contingently true proposition might not have an explanation of the sort one is demanding (it is no objection to the PSR that not every contingent truth has a biological explanation). For the PSR does not say that every contingently true proposition has an explanation of every sort one could demand, but only that it has an explanation.

So, if the above is right, there really are no contrastive propositions that demand special kinds of explanations. Compare the following two demands for explanation:

  1. Why did George eat the banana?
  2. Why did George eat the banana?
I do not think many will want to multiply propositions to the point that we have the following multiplicity of propositions:
  • that George ate the banana
  • that George ate the banana
  • that George ate the banana
  • that George ate the banana
A plausible thing to say is that there is only one proposition that (3) and (4) both demand an explanation of, the proposition that George ate the banana (are there italics in the Platonic heaven?), but that the italics specify contextually what explanations would be accepted. It seems very plausible that the phenomenon of emphasis in the demand for explanation is essentially the same phenomenon as the use of "rather than". Indeed, we might even be able to paraphrase (3) as:
  1. Why did George eat the banana rather than doing something else with it?

There is one more point to be made (which I basically got from Josh Rasmussen). Sometimes in a report of a choice, the "rather than" occurs in the content of the choice. Thus, someone may choose to eat the banana rather than the orange or, perhaps equivalently, choose to eat the banana over eating the orange. In this case, the content of the choice is contrastive. But a choice with a contrastive content does not demand a contrastive explanation in any sense problematic for the PSR. For there may well be a reason for someone making a contrastive choice—for instance, they may normally eat oranges, but be making a political statement by eating the banana rather than the orange (maybe orange is the color of one political party and yellow that of another). In this sense, there is a difference between:

  1. George chose to (eat the banana rather than the orange)
  1. George chose to eat the banana rather than choosing to eat the orange.
In (7), it is implicated or presupposed or maybe even stated (though I don't think so) that George could have chosen to eat the orange. But no claim is made in (7) that George deliberated between the banana and the orange, nor that he mentally compared them, nor that his chose of the banana was made under a description that said anything about oranges. (Maybe (7) holds because George didn't realize the orange was even an option.) On the other hand, (6) is only true when both the banana and the orange entered into George's deliberation, and he chose the banana under a description that included something like "alternative to an orange". And then we can give a reason, perhaps a non-contrastive one.

1 comment:

Adrian Woods said...

The truth of PSR should not be contingent upon our ability in any particular instance to identify or articulate an explanation. Right?