Thursday, October 08, 2009

Smith on Parfit: 9 of 15: The Rationality of Desire

In this series of posts I am commenting on an article sent to me by a member of the studio audience. These are, in a sense, notes written in the margin as it were as I highlight passages in the article and explain my agreement or disagreement.

I am looking at some principles of what reason is thought to require that Smith presented in the article. In Part 8, I argued that a desire-as-end that P and a belief that bringing about Q will bring about P only generates a belief in a desire-as-means that Q. An actual desire-as-means that Q requires that the belief is true.

Another principle that Smith mentions is:

If someone has an intrinsic desire that p, and an intrinsic desire that q, and an intrinsic desire that r, and if the objects of the desires that p and q and r cannot be distinguished from each other and from the object of the desire that s without making an arbitrary distinction, then she has an intrinsic desire that s.

I think I agree. However, is this actually a relationship among desires, or a relationship among sentences?

How are we supposed to take the claim that p, q, and r cannot be distinguished from each other?

One option that I can think of is that p, q, and r are the same sentence written in three different languages. In this case, a desire that p is identical to a desire that q and a desire that r because the proposition p is identical to the propositions q and r. They are merely being expressed using different words.

This raises an interesting question about logical entailments of proposition. For example, if an agent desires that P, and P implies Q (where we are talking about logical implication here, not material implication), then does it follow that the agent desires that Q?

I had not thought about this question before but, upon thinking about it, I see some problems. For example, P and Q implies P, but a desire that P-and-Q, it seems on first blush, does not necessarily imply a desire that P or a desire that Q.

However, in the case where P is logically identical to Q, it does appear to be true that a desire that P implies a desire that Q.

Yet, in this case I fail to see this as a principle of the rationality of desirs. I see it as an example of a case where a desire that P is identical to a desire that Q where P is identical to Q. It is a principle of the rationality of propositions, where it just so happens to be the case that in speaking about desires we are speaking about propositional attitudes. Of course it is the case that if we are talking about attitudes towards propositions then we are talking about attitudes towards those entities that have the properties of propositions.

1 comment:

Thom said...

Suppose that I am a computer scientist. Can I desire that one problem is easy and another hard when the two are equivalent? Could I desire that the Axiom of choice be true and that the Well-Ordering Principle be false? Could I desire that the Peano axioms be consistent, complete, and decideable? Does it matter if that I am aware of the inconsistency?

I see no trouble with holding desires that are logically contradictory. It would simply be impossible to fulfill both of them, a situation that is quite common when practical constraints are added into the picture. If given a choice between fulfillment of logically inconsistent desires, an agent would act so as to fulfill the stronger desire, just as with practically inconsistent desires.