  Mendelssohn worked within the framework of Wolffian metaphysics and psychology, and thus he accepted the definition of sensible perception as clear but confused cognition. He accepted Wolff’s explanation that pleasure arises in the sensible perception of perfection, but also Baumgarten’s transformation of that formula into the explanation of beauty as the perfection of sensible cognition: in Mendelssohn’s terms, “the essence of the fine arts and sciences consists in an artful, sensibly perfect representation or in a sensible perfection represented by art” (“On the Main Principles of the Fine Arts and Sciences” (1757), Philosophical Writings, pp. 172–3). But Mendelssohn vigorously rejected any interpretation of the Wolffian premise according to which the confusion of sensible perception itself could be the source of our pleasure in it. For Mendelssohn, any “pure gratification of the soul must be grounded in the positive powers of our soul and not in its incapacity, not in the limitation of those original powers” (On Sentiments, Fourth Letter; Philosophical Writings, p. 19). Further, “neither fully distinct nor fully obscure concepts are compatible with the feeling of beauty”: beauty requires that an object offer enough “extensive clarity,” that is, richness and variety, to stimulate us, but enough unity so that we can easily take it in as a whole (On Sentiments, Third Letter, Philosophical Writings, pp. 14–15). Mendelssohn’s explicit thesis is that while the parts of an object must be distinct enough to allow one to have a sense of their variety but dense enough to allow one to grasp them together with equilibrium and proportion, it is the latter that is the source of our pleasure.  It might seem a stretch to read him as also suggesting that it is the play of the mind back and forth between its perception of the parts and its grasp of the whole that is pleasant.  But he will argue that the exercise of various of our powers, indeed as we are about to see bodily as well as mental powers, is itself a perfection that we enjoy, so this might at least point toward the idea that the source of pleasure in beauty is the free play of the those powers.