 Mendelssohn’s “On Evidence in Metaphysical Sciences” (the so-called Prize Essay) garnered first prize in the contest staged by the Royal Prussian Academy of Sciences on the question of whether metaphysical truths are able to have the same sort of evidence as mathematical truths. (An essay by Immanuel Kant came in second place.) In the essay, published in 1763, Mendelssohn argues that metaphysics pursues its subject matter by applying the same method that mathematics does: conceptual analysis. As he puts it, “The analysis of concepts is for the understanding nothing more than what the magnifying glass is for sight” (Philosophical Writings, p. 258). But Mendelssohn then proceeds to differentiate the kinds of evidence in mathematics and in metaphysics in the following way. Like calculus, but unlike geometry, metaphysics works with concepts that are no less certain than those of geometry, but lack the transparency and imaginative resources available to the geometer’s concepts. The difference between mathematics and metaphysics lies in the difference in the content of the concepts, namely, the difference between quantity and quality. At the same time, there is a basic harmony between the two disciplines since quantity and quality are both intrinsic characteristics of finite things and neither quantity nor quality exists without the other (though qualities and not quantities are allegedly conceivable without some other thing).