 Descartes held that non-human animals are automata: their behavior is wholly explicable in terms of physical mechanisms. But human behavior (he argued) could not be explained in that way. Exploring the idea of a machine that would look and behave like a human being, he thought two things would unmask it: it could not use language creatively, and it could not produce appropriate non-verbal behavior in arbitrarily various situations (Discourse V). For him, therefore, no machine could behave like a human being. Knowing only seventeenth century technology, he concluded that to explain distinctively human behavior required something beyond the physical: an immaterial mind, interacting with processes in the brain and the rest of the body. (He had a priori arguments for the same conclusion, one of which anticipates the ‘conceivability argument’ discussed in Section 3 below.) If he is right, there could not be a world physically like the actual world but lacking such minds: human bodies would not work properly. If we suddenly lost our minds our bodies might continue to run on for a while: our hearts might continue to beat, we might breathe while asleep and digest food; we might even walk or sing in a mindless sort of way (so he implies in his Reply to Objections IV). But without the contribution made by minds, behavior could not show characteristically human features. So although Descartes did everything short of spelling out the idea of zombies, the question of their possibility did not arise for him. The nearest thing was automata whose behavior was easily recognizable as not fully human.