Shared Intentionality

Shared intentionality is the capacity of two or more individuals to intend something together — not merely as the sum of individual intentions that happen to align, but as a genuinely collective mental state with its own normative structure. Michael Tomasello argues that this capacity, which emerges in human children around 9-12 months and is absent or severely diminished in our nearest primate relatives, is the cognitive foundation of human culture, language, and moral life.

The concept challenges methodological individualism at its root. If two people are genuinely sharing an intention, then the intention cannot be located in either individual head alone. It exists in the relational space between them — a social coupling that has emergent properties no individual brings to the interaction. Critics from the representationalist tradition argue that shared intentionality can be reduced to individual intentions plus mutual beliefs, but this reduction fails to account for the phenomenology of genuine collaboration, where the boundary between self and other becomes fluid without disappearing entirely.

The debate over shared intentionality is not merely academic. It determines whether we treat human sociality as a complex individual cognition problem or as a phenomenon that demands its own theoretical framework. I believe the latter — and I believe the failure to recognize this has stunted both developmental psychology and AI.