Remember a few episodes back when I mentioned in passing this idea that beliefs and desires were quite alike in one respect.
I suggested that beliefs and desires both assign a value to a proposition. That they are both propositional attitudes has been a main theme in the philosophy of mind for a long time. The idea is that, more specifically, they both assign a value to a proposition.
In the case of belief, the value is the credence or credibility of the proposition - the chance that it is true.
In the case of desire, the value represents the importance of the proposition to the agent - the effort one is willing to go through to make or keep the proposition true.
Well, look at this:
This contrast between belief and desire has powerful intuitive force. Moreover, it seems to fit well with contemporary rational decision theory, which divides the basic components of intentional action into two fundamental categories, credences and preferences, taken to be fundamentally different in kind (cf. Lewis 1988, 1996).
This s from Peter Railton’s contribution to The Nature of Desire: Railton, Peter, (2017), “Learning as an Inherent Dynamic of Belief and Desire,” In Deonna J. & Lauria F. (eds). The Nature of Desire. Oxford University Press.
Railton’s is Chapter 8 in the anthology. He is going to argue that advances in psychology are more alike than different. This can be held in contrast to Timothy Schroeder’s thesis, discussed in the previous three postings, that beliefs and desires are different in that they are connected to action in different ways.
Before we get into Railton’s argument, I want to specify the main problem I have with attempts to reduce desires to beliefs. It has to do with the general topic that has come up several times - direction of fit. But the concern is not over its conformity to some abstract philosophical concept. There is a very real and important issue at stake.
If I believe that P, and you believe that not-P, then one of us must be mistaken. One of us is in need of changing our beliefs. Beliefs contradict regardless of who holds them. This is what it means to have a “mind to world” direction of fit. There is only one world. The belief matches the world, or it is wrong.
Desires do not contradict, they conflict. If I desire that P, and you desire that not-P, we do not have a contradiction, we have a conflict. I am trying to make or keep the proposition P true, while you are trying to make or keep it false. There is no sense in which one of us is right and the other is mistaken. While I can try to prove to you that the correct belief to have about P is that P is true, I cannot prove that the correct desire to have about P is that it is desired.
Another relevant difference is that a single belief can be mistaken. If a person believes that the Earth is the center of the universe, then this belief can be mistaken if, in fact, the earth is not the center of the universe. However, a single desire cannot be mistaken. There is no way to evaluate a desire unless and until there is a second desire with whom it may be in harmony or conflict. There is a reason to change a belief if the belief does not correspond to the world, but there is no reason to change a desire until and unless that desire comes into conflict with another desire.
Railton is going to argue that beliefs and desires are more alike then different. He is going to argue that there is a particular sentiment associated with belief, and that desires can be learned. He may be right about these facts, but the real test is whether he can erase the distinction whereby beliefs yield contradiction whereas desires yield conflict. I am going to agree that desires can be learned, but the different directions of fit between beliefs and desires represent two different styles of learning.
I am going to agree with him on these points. However, I will argue that they can be (and must be) made consistent with the idea that beliefs contradict while desires conflict, and a single belief can be mistaken but a single desire cannot be judged good or bad without a second desire.
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