 The second proof establishes the same basic law but does so “a priori” on the basis of the “mere definition” of an entity with free will. The choices made by such an entity are based upon what it finds pleasing, namely, “the perfection, beauty, and order” that it perceives or believes that it perceives in the preferred objects. With their unmistakably aesthetic accent, these qualities serve as “motivating grounds” (Bewegungsgründe) to act or refrain from acting. Without being physically coercive, these motivating grounds entail an “obligatoriness” or “moral necessity,” since no free spirit could enjoy the opposite of them. This proof has been recently challenged in at least two, complementary ways (Klemme 293). First, if a free, rational person necessarily chooses to act in accordance with her knowledge of good and evil, how can she be required to perfect herself? Second, why is the law normative and not merely descriptive? These are significant objections but they arguably suppose positions that neither Mendelssohn, the proponent of common sense, nor Mendelssohn, the metaphysician, can countenance. By underscoring the imperfection but also the corrigibility of reasonable people, common sense insures the meaningfulness of the injunction to self-perfection. From a metaphysical description of the basis (motivations, ends) of a rational choice, normative constraints follow for making precisely those sorts of choices.