 By way of introducing the last segment of this discussion of evidence in ethics, Mendelssohn distinguishes theoretical and practical forms of approval. While it is impossible to doubt what is a matter of intellectual conviction, it is possible for us to act contrary to an obligation that we are convinced of. So, too, some truths are intellectually convincing but do not move us, whereas other, less certain truths do so, producing “lively and efficacious” cognition, passing over into the faculty of desire, and even motivating decisions. The familiar reason for this discrepancy in the efficaciousness of truths is, Mendelssohn, submits, the recalcitrance of inclinations to reason. Approval of a truth becomes practical if the rational principles either gain the upper hand over inclinations or put them to its advantage. Mendelssohn identifies ethics’ four means of securing the agreement of reason and desire: (1) increasing the number of motivations, (2) practice and habit, (3) adding pleasant sensations (for which art and literature are particularly useful), and (4) examples that have been observed or can be intuited (e.g., history, Aesop’s fables).