<p>Across the cognitive sciences, researchers have studied theory of mind (making sense of other people’s behaviours in terms of their mental states, or ‘naive psychology’) and physical reasoning (making sense of physical events in terms of their underlying mechanics and dynamics, or ‘naive physics’), as two separate processes. In this Perspective, we describe two ways in which psychological reasoning depends on physical reasoning. First, people represent the bodies of animate agents as objects, and their actions as physical events. Second, people use physical knowledge to make inferences about other minds, including what other people want, feel and know, how hard they are trying, and how much danger they are in. We review research from developmental psychology and cognitive neuroscience that provides evidence for the interaction between these two systems, and Bayesian computational models of theory of mind that articulate a formal hypothesis about how they work together. We propose that from early in human development people navigate the social world by using two distinct but interacting systems for reasoning about other agents’ ethereal minds and their physical bodies.</p>