It is possible in principle to build a machine that behaves exactly like a human being but has no consciousness or intentionality. No mental life at all. ... So the possibility in principle of a zombie that behaves just like a human being seems to me something that cannot be ruled out a priori. It is no doubt difficult and perhaps impossible in practice, but in theory it is easy to imagine such a machine.
My own view is that this radical incompleteness of natural science with respect to consciousness entails, at the minimum, an equally radical agnosticism about the ontology of minds and persons. ... We might, after all, be zombies.