Abstract
At the heart of the social intelligence hypothesis is the central role of 'social living'. But living is messy and psychologists generally seek to avoid this mess in the interests of getting clean data and cleaner logical explanations. The study of deception as intelligent action is a good example of the dangers of such avoidance. We still do not have a full picture of the development of deceptive actions in human infants and toddlers or an explanation of why it emerges. This paper applies Byrne & Whiten's functional taxonomy of tactical deception to the social behaviour of human infants and toddlers using data from three previous studies. The data include a variety of acts, such as teasing, pretending, distracting and concealing, which are not typically considered in relation to human deception. This functional analysis shows the onset of non-verbal deceptive acts to be surprisingly early. Infants and toddlers seem to be able to communicate false information (about themselves, about shared meanings and about events) as early as true information. It is argued that the development of deception must be a fundamentally social and communicative process and that if we are to understand why deception emerges at all, the scientist needs to get 'back to the rough ground' as Wittgenstein called it and explore the messy social lives in which it develops.