My aim in this paper is to show how confusion and unclarity about reasons for action has led to serious error in ethics and the philosophy of action, and to try to set matters right. In Part I I set out what reasons for doing are, and try to make clear the distinction between reasons as justifying actions and reasons as motivating them. In Part II I try to show how, even in the ideal situation of successful and correct deliberation, (...) a justifying reason is never identical with a motivating one, since they are two quite different sorts of thing. However a motivating reason and what one takes to be a justifying reason may be the same. In Part Ill I show how failing to make these distinctions leads to paradoxes and absurdities in the philosophy of action. It emerges that a related distinction must be made between wanting, valuing, and being valuable. (shrink)