The problem of other minds is a problem of modern philosophy that can be traced back to the French seventeenth century philosopher René Descartes. Descartes held the dualistic view that, apart from God, there are two kinds of things (or "substances") in the world: "extended things" and "thinking things". He thought, in particular, that a human being is a union of an extended thing (a body) and a thinking thing (a mind). He recognized that, given such a view, an account has to be given of how these two fundamentally different things are united, and in particular, how there can be causal interaction between them. But Descartes does not seem to have fully realized that another sort of issue needs to be addressed as well. Consider the following passage from Descartes' Meditations on First Philosophy: if I look out the window and see men crossing the square, as I just happen to have done, I normally say that I see the men themselves […]. Yet do I see more than hats and coats which would conceal automatons? I judge that they are men. (Descartes 1984, 21)