Prudence and the reasons of rational persons

Hume said that the reasons that determine the rationality of one's actions are the desires one has when acting: one's actions are rational iff they advance these desires. Thomas Nagel says this entails calling rational, actions absurdly conflicting in aims over time. For one might have reason, in one's current desires, to begin trying to cause states one foresees having reason, in one's foreseen desires, to prevent. Instead, then, real reasons must be timeless, so that current and foreseen reasons cannot conflict. I say the desire theory does not have absurd consequences. A rational agent's desires would rationally evolve, never requiring actions conflicting in aims over time, except where it was instrumentally rational for her to change in her desires, whence such conflicts are rationally appropriate. Further, whatever sorts of things count as real reasons, since reasons can rationally require their own revision, they cannot be necessarily timeless.