The quantum semantics literature has focused on individuals in isolation; I want now to extend it to the more realistic case of dialogue. Here it is not only neighboring words and sentences that form the context of speech acts, but the presence of other people with their own intentions. In shifting to interaction we run up against the Problem of Other Minds. Philosophers actually distinguish two such problems: an epistemological or “mind-reading” problem of knowing what others are thinking; and a deeper problem of knowing whether others have minds at all. However, for social scientists the main issue is mind-reading, on which there is a substantial literature in psychology, and I shall limit my focus accordingly below.

It is widely agreed that people are quite good at mind-reading; the question is how we do it, given the apparent privacy of consciousness. The dominant answer is that the mechanism is representational, inferential, and therefore “indirect.” On this view, each of us has a “Theory of Mind” in our heads, which by analogy to a scientific theory represents others' minds well enough that we can infer their thoughts. Advocates of “direct perception” have challenged this picture, arguing that what we see in encounters with others is not representations of their minds in our heads, but their minds themselves in action. Both sides, however, assume that our minds are classical and therefore separable systems. This is particularly problematic for the direct perception account because it means that our contact with others' minds is subject to the constraints of local causality and as such cannot literally be direct.

I shall approach this problem indirectly, by way of how we visually perceive material objects. I do so for two reasons. First, the literature itself is preoccupied with the visual aspects of mind-reading, and as such curiously has not made language a central theme. There has been work on how learning language is important for developing children's mind-reading abilities, and of course much on expressive behavior, most of which is linguistic.