In the not too distant future, we will be able to construct artificial systems that give every appearance of consciousness—systems that act like us in every way. These systems will talk, walk, wink, lie, and appear distressed by close elections. They will swear up and down that they are conscious and they will demand their civil rights. But we will have no way
to know whether their behavior is more than a clever trick—more than the pecking of a pigeon that has been trained to type "I am, I am!"
We take each other's consciousness on faith because we must, but after two thousand years of worrying about this issue, no one has ever devised a definitive test of its existence. Most cognitive scientists believe that consciousness is a phenomenon that emerges from the complex interaction of decidedly nonconscious parts (neurons), but even when we finally understand the nature of that complex interaction, we still won't be able to prove that it produces the phenomenon in question. And yet, I haven't the slightest doubt that everyone I know has an inner life, a subjective experience, a sense of self, that is very much like mine.
What do I believe is true but cannot prove? The answer is: You!