  Mendelssohn never presented his aesthetic theory in a full-length treatise. His most systematic presentation, the 1757 essay “On the Main Principles of the Fine Arts and Sciences,” discusses only three out of the four axes of potential perfection that he finds in the complete aesthetic experience. We therefore need to supplement what we can glean from this essay with suggestions from On Sentiments and the Rhapsody, or addition to the Letters on Sentiments that he added to his 1761 collection. The four axes that Mendelssohn identifies are the perfection in the object of the aesthetic experience, typically the perfection of what is depicted by a work of art but not always, since some arts, such as music and architecture, and all of nature are not mimetic at all; the perfection of our own perceptual capacities in the experience of an object, the “perfection of sensible cognition” that he adopted from Baumgarten; the perfection of our bodily condition that can be produced through the effect of our mental condition on our body, a dimension lacking from all previous accounts in the German rationalist tradition but perhaps inspired by Mendelssohn’s acquaintance with Edmund Burke’s account of the physiology of our feelings of the beautiful and the sublime (itself perhaps building upon the common property of David Hartley’s 1749 Observations on Man); and finally, the perfection of the artistry that has gone into the production of an object, whether human artistry in the case of a work of art or divine artistry in the case of the beauties of nature. Perfection along any of these axes is a potential source of pleasure in the experience of an object, and the effect of these sources of pleasure can be additive, each increasing our pleasure in the same object. But these multiple dimensions to our pleasure in objects also create the possibility of the “mixed emotions” that we experience in the artistic representation of unpleasant or tragic objects, because in those cases our pleasure in the mental activity stimulated by the work of art, the pleasant effect of that on the body, and our admiration of the artistry that has gone into the object can outweigh any pain associated with the depicted content of the work.