This paper offers one formal reason why it may often be inappropriate to hold, of two conflicting desires, that the first must be weaker than, stronger than, or of the same strength as the second. The explanation of this fact does not rely on vagueness or epistemological problems in determining the strengths of desires. Nor does it make use of the problematic notion of incommensurability. Rather, the suggestion is that the motivational capacities of many desires might best be characterized by two values, neither of which should be interpreted as strength.