It is now over twenty years since Premack and Woodruff (1978) posed the question, ‘Does the chimpanzee have a theory of mind?‘—’by which we meant’, explained Premack (1988) in a later reappraisal, ‘does the ape do what humans do: attribute states of mind to the other one, and use these states to predict and explain the behaviour of the other one? For example, does the ape wonder, while looking quizzically at another individual, What does he really want} What does he believe? What are his intentions?’

That chimpanzees, and indeed other primates, might operate in this way came to be seen as a promising conjecture in the light of parallel studies of primate societies in the wild. It was never entirely clear why the laboratory scientists Premack and Woodruff asked their famous question, other than to express curiosity about one further respect in which an ape might be more like a human than had been acknowledged. But primate ethology offered a deeper rationale for suspecting the existence of something like a non-human theory of mind. Monkeys and apes were found naturally to interact with unsuspected sophistication. They were shown, for example, to build and exploit relationships with allies (Harcourt and de Waal, 1992) to deceive and counter-deceive (Whiten and Byrne, 1988a) and to repair beneficial relationships after over-enthusiastically denting them (de Waal, 1989; Castles and Whiten 1998a & 1998b). The emerging complexity of primate sociality was indicated by book titles like Chimpanzee Politics (de Waal, 1982) and Machiavellian Intelligence (Byrne and Whiten, 1988 Whiten and Byrne, 1997).