It is widely assumed that Kant’s moral psychology draws from the dualist tradition of Plato and Aristotle, which takes there to be distinct rational and non-rational parts of the soul. My aim is to challenge the air of obviousness that psychological dualism enjoys in neo-Kantian moral psychology, specifically in regard to Tamar Schapiro’s account of the nature of inclination. I argue that Kant’s own account of inclination instead provides evidence of his commitment to psychological monism, the idea that the mentality of an adult human being is rational through and through. I first consider Schapiro’s “intuitions” in favour of dualism: inclination must have a non-rational source, she contends, because they assail us unbidden and are not immediately responsive to volition, and because we are not responsible simply for having inclinations (only for acting on them). I explain how a monistic account of the nature of inclination can accommodate the first two points, and explain why the third neither is a point a Kantian can accept, nor is its denial the affront to common sense that Schapiro supposes. Then I turn to Schapiro’s aim to conceive of reflection as non-rational and thus independent of justificatory thought, and yet such as to induce rational reflection. I argue that it remains mysterious how inclination, on her account, could be resourced to play this role; and with that criticism in mind, I conclude by making a positive case for Kant’s conceiving of inclination in monistic terms, as an expression of rational mindedness.