Western philosophers often see something puzzling about knowing another person's “inner” meanings when one has access only to behavior: This is the “other minds” problem (Austin, 1959). William James noted: “Our senses only give us acquaintance with facts of the body, and … of the mental states of other persons we have only conceptual knowledge” (1890, pp. 222-223); Ludwig Wittgenstein argued: “When we communicate a feeling to someone, something which we can never know happens at the other end. All that we can receive from him is an expression” (1965, p. 185).

This chapter describes a spontaneous communication process in which expressive behaviors constitute “facts of the body” that are veridical signs of motivational-emotional states. Given attention, these expressive behaviors provide all we need to know about what has happened at “the other end.” It is argued that communication proceeds in two simultaneous streams: a symbolic stream, which is learned, intentional, and prepositional; and a spontaneous stream which is biologically based, direct, nonpropositional, and based on subcortical and paleocortical brain systems. The chapter presents spontaneous communication as the basis of the interpersonal self, and summarizes relevant research in a variety of subject groups.