To know and to interact with other people requires predicting their actions, their reactions to one's own actions, and their interactions with other social beings, including oneself. The focus of this chapter is on the psychosocial knowledge required for successful interactions. Social beings are complex and their behavior is not entirely predictable; so also are some physical phenomena. But in coming to understand nonsocial objects, predictions about the behavior of those objects may be made with out concern for how those predictions may themselves alter the behavior of the objects. For example, predicting the weather is inherently fallible, because the system is so complex that very minor perturbations can have major unanticipated effects. But the predictions of weather scientists are not part of the system, and actions emanating from them do not affect the behavior of the system in any way. In contrast, a person within a social group of two or more people acts always with the knowledge that her own action may influence the actions of others in ways that she must be able to predict if she is to act intelligently.

As outlined in Chapter 4, implicit knowledge of other people in relation to oneself begins in early infancy, as the child takes her place in the social world. Intelligent action, affective responsiveness, and communicative signals in response to others can be traced throughout the first two years.