That's the big question. What do we mean by conscious? I think the key thing is qualia. That is, there's some subjective experience. If you prick us, not only

That's the big question. What do we mean by conscious? I think the key thing is qualia. That is, there's some subjective experience. If you prick us, not only do we bleed, but we feel it. This is pretty vague, which is the whole problem. But if you feel it when you're pricked, you know what I'm talking about. This can't be measured or even observed except from the inside. Nobody even has the slightest idea of how it could be measured, even theoretically. The existence of this phenomenon in people other than myself is something I have to take largely on faith. (But, as I mentioned, not entirely, since the existence of this concept shows at least some other people have it.)