It is surely a sign of intellectual progress that a discussion of consciousness need no longer begin with a debate about its existence. To say that consciousness may only seem to exist, from the inside, is to admit its existence in full—for if things seem any way at all, that is consciousness. Even if I happen to be a brain in a vat at this moment—and all my memories are false, and all my perceptions are of a world that does not exist—the fact that I am having an experience is indisputable (to me, at least). This is all that is required for me (or any other sentient being) to fully establish the reality of consciousness. Consciousness is the one thing in this universe that cannot be an illusion.