 Mendelssohn’s ethics is a form of perfectionism, resembling the rationalist perfectionism of Christian Wolff’s ethics but also significantly departing from it in ways that echo Mendelssohn’s appreciation of aesthetic and affective dimensions of moral life. In the fourth and final part of his Prize Essay, Mendelssohn investigates the extent of evidence in the foundational principles of ethics (Anfangsgründe der Sittenlehre) and, in particular, how it compares to evidence (“the certainty and comprehensibility”) of geometry’s basic principles. He introduces the discussion with the observation that when someone undertakes the right sort of action, that person “tacitly” makes the following “rational inference,” a moral syllogism in the form of a modus ponens: