Definition
Theory of mind (ToM) is the cognitive capacity to attribute independent mental states — beliefs, desires, intentions, emotions, knowledge — to oneself and to other agents, and to understand that those mental states may differ from one's own and from reality, thereby enabling prediction and explanation of others' behavior.
The term was introduced by primatologists David Premack and Guy Woodruff in 1978 in their paper asking whether chimpanzees had a "theory of mind" — that is, whether they could represent mental states at all. In developmental psychology it is most associated with the false-belief paradigm introduced by Wimmer and Perner (1983). Goleman treats ToM as the cognitive infrastructure of other focus: you cannot truly attend to another person's inner world without first representing that they have an inner world distinct from yours.
Why it matters
How it works
The false-belief task
Wimmer and Perner's 1983 "Maxi" task — and its more widely replicated successor, Baron-Cohen, Leslie, and Frith's "Sally-Anne" task (1985) — became the standard developmental test for ToM acquisition. A child watches a scene: Sally places a marble in a basket and leaves; Anne moves the marble to a box while Sally is away. Where will Sally look for her marble? Children under approximately 4 consistently say "in the box" — where the marble actually is. Children over 4 say "in the basket" — where Sally believes it to be. The shift represents the emergence of the capacity to represent a belief that is false — distinct from one's own knowledge of reality.
The mentalizing network
Neuroimaging has localized a consistent network active during ToM tasks: the temporoparietal junction (TPJ, especially right-lateralized), the medial prefrontal cortex (mPFC), the posterior superior temporal sulcus (pSTS), and the anterior temporal lobe. These regions activate when a person attributes mental states to others, reads intentional action, or processes social narratives. The TPJ, in particular, shows specificity for third-person mental-state attribution across many experimental contrasts.
Levels of ToM and the stacking problem
ToM operates recursively. First-order ToM: "Sally thinks the marble is in the basket." Second-order: "Anne knows that Sally thinks the marble is in the basket." Third-order: "I know that Anne knows that Sally thinks..." Most social situations require only first- and second-order ToM. Complex negotiations, alliance politics, and theory of chess require third-order and higher. The recursive stack is cognitively demanding; working memory capacity constrains how deep an agent can reliably go.
Autism and the "mindblindness" hypothesis
Simon Baron-Cohen's 1995 book Mindblindness proposed that autism spectrum conditions involve delayed or disrupted development of the mentalizing system — a difficulty in automatically and spontaneously attributing mental states to others. The evidence is robust at the level of standard ToM tasks (Sally-Anne, Eyes test, advanced ToM); the precise neural mechanism remains debated. Baron-Cohen and others now prefer "different cognitive style" framings that acknowledge mentalizing differences without characterizing autism as a deficit in all social domains.