Here are three things I would like:
- Not to be kidnapped by aliens today for medical experiments.
- To own the Hope Diamond.
- To own a minivan.
So when we talk of the strength of a desire we are being ambiguous between talking of the intensity of the feeling and degree of preference. One might think of the degree of preference as something like a part of the content of the desire—the desire representing the degree to which one is to pursue something—while the intensity of the feeling is external to the content.
Those of us who think of emotions in a cognitive way, and who think there are many normative facts about what emotions one should have given one's situation, may be tempted to think that the intensity of the feeling should match the degree of preference. But that is mistaken. There are perfectly good reasons why my desire for the Hope Diamond and for not being kidnapped by aliens today should be less intensely felt than my desire for a minivan. The minivan is an appropriate object for my active pursuit, for instance, while I have little hope of getting the Hope Diamond and little fear of being kidnapped by aliens.
Maybe, then, the intensity of the desire should be proportional to the role that the desire should play in one's pursuits? That's an interesting hypothesis, but not clearly true. Let's say that you are told that you will be executed if and only if 29288389−1 is prime. At this point it seems quite right and proper to have an intense that this number not be a prime. But there is nothing you can do about it; barring Cartesian ideas about God and mathematics, there is no pursuit that you can engage in that can make it more or less likely that the number is a prime.
A better story would be that the intensity of the desire should be proportional to some kind of a salience. One way of the desire being salient is that it should play a heavy role in one's present pursuits. But there may be other ways for it to be salient.
There is, anyway, a spot of spiritual comfort in all this. Sometimes people worry that they do not desire God as much as they desire earthly things. But a distinction must be made. Preferring earthly things to God is clearly bad. But having a more intense desire for an earthly thing than for God may not always be a bad thing. For sometimes one must focus on an earthly task for God's sake, and a means can be more salient than the end.