Rousseau's thought is marked by an optimism and a pessimism that each evoke, at least in the right mood, a feeling of recognition difficult to suppress. We have an innate capacity for virtue, and with it freedom and happiness. Yet our present social conditions instill in us a restless craving for superiority, which leads to vice, and with it bondage and misery. Call this the thesis of possible goodness: that while human psychology is such that men become wicked under the conditions in which we now find them, nevertheless men would be, or have been, good under other conditions. It is surprisingly difficult, or at least surprisingly complicated, however, to articulate even a possible psychology that would explain the thesis of possible goodness. Interpretations of Rousseau, even several to which the author of this essay is highly indebted, have not fully engaged, I think, with the complications. This essay tries to reconstruct psychological principles that would explain the thesis and that are at least consistent with what Rousseau otherwise says on the subject. Much of the value of this exercise, however, lies not in the particulars of the resulting psychology but rather in the depth of the tension between Rousseau's optimism and his pessimism that it reveals.