Abstract
It is widely accepted that the more you desire something, the more it would be rational for you to pursue it. This idea is also often formulated in terms of the following principle: The Strength Principle: Rationality requires of you that you take the means to satisfy your strongest desire.
In this paper, however, I am going to cast some doubt on the prescriptive force of the Strength Principle. I first distinguish between three alternative conceptions of desire strength: desire strength as the decision-theoretical notion of utility, as phenomenological intensity, and as motivating power. As I argue, desire strength as utility lacks prescriptive force because it tracks what we ended up choosing and pursuing, while desire strength as phenomenological intensity has derivative rational relevance only because it often indicates which desire can bring about greater pleasure within us. I then challenge the prescriptive relevance of desire strength as motivating power by considering the following example: As you are removing the damaged unit from the external solar panels on your spaceship, you exert too much force and accidentally detach yourself from the cord that connects you and the spaceship. You cannot help but find yourself gradually pulled away from your spaceship and toward the green planet far on the horizon. You are desperate at first, but you then think that you would rather drift toward somewhere than float aimlessly in space forever anyway. You then hear a strange voice from the audio system in your spacesuit: "You're entering our realm. We require you to move toward our green planet".
There is something peculiar about the requirement issued to you. You are already being pulled toward the green planet and cannot help anyway, so the requirement seems futile because your following it cannot be what brings about the required act in the first place. Furthermore, you would rather go to the green planet than anywhere else. So the disappearance of this requirement in your thought would not make any difference. Indeed, it can be argued that the best way to bring about the required act is just for this requirement to disappear in your thought. Can this requirement be a valid prescription for you? No. And I contend the same is the case with the Strength Principle.