To make sense of the social world, people reason about others’ mental states, including whether and in what ways others can form new mental states. We propose that people’s judgments concerning the dynamics of mental state change invoke a “naive theory of reasoning.” On this theory, people conceptualize reasoning as a rational, semi-autonomous process that individuals can leverage, but not override, to form new rational mental states. Across six experiments, we show that this account of people’s naive theory of reasoning predicts judgments about others’ ability to form rational and irrational beliefs, desires, and intentions, as well as others’ ability to act rationally and irrationally. This account predicts when, and explains why, people judge others as psychologically constrained by coercion and other forms of situational pressure.