 As Descartes defines it, virtue depends upon the employment of reason. Though it is conceivable that one might have a “firm and constant will” to do something without having examined whether it is the right thing to do, one cannot have a firm and constant will to do what is judged to be the best, unless one is capable of judging what the best is. Thus, virtue presupposes knowledge of the relative goodness of objects of choice, and this knowledge Descartes assigns to reason: “The true function of reason… is to examine and consider without passion the value of all the perfections, both of the body and of the soul, which can be acquired by our conduct, so that… we shall always choose the better” (AT IV 286–7/CSMK 265).