There is an old joke: to find out if a computer is conscious, you program it to tell the truth, and you ask it if it is. The point behind the joke is deep, I think. If we made a computer, we would know how we could make it correctly report sensor data like the current temperature whether outside or inside the computer. But how would we make it sense whether or not it is conscious?
If had a consciousness sensor, we could do some nice experiments on the nature of consciousness. We could, for instance, test naturalistic hypotheses that consciousness is the product of the appropriate kinds of complexity of data processing.
But it turns out that we do have a tool here. We are blessed with having unconscious thought in addition to conscious thought, and we can tell the two apart. Of course, we can only indirectly discern the presence of unconscious thought—but once we’ve learned that a thought process occurred, then we can use introspective memory to check (fallibly) whether it was conscious or not.
Does this tool provide any useful data? I think so. For instance, it empirically verifies the premise of this one-premise argument:
Some of our unconscious thinking is just as sophisticated as some of our conscious thinking.
So, consciousness is not the product of the sophistication of our thinking.
Of course, only a very incautious naturalist would hold that consciousness is the product of the sophistication as such of our thinking. But, still, it’s pretty nice to have an empirical argument here.
Similarly, we can rule out the hypothesis that consciousness is a function of sophisticated irreducibly first-person thought, since it is clear that our unconscious thought is deeply concerned with first-person issues, and in sophisticated ways. Likewise, I suspect, we can rule out the hypothesis that consciousness is a function of sophisticated second-order thought or even sophisticated second-order irreducibly first-person thought. A primary way in which we detect unconscious thinking is when we suddenly come to a conclusion “out of nowhere”. The difficulty of reaching that conclusion is evidence of the sophistication of the thought process that led to it. And I think that such eureka moments can happen in all subject matter, including that of second-order irreducibly first-person thoughts.
This makes the challenge for naturalist theorist of mind tough: they need to identify as the basis of consciousness a type of mental processing that cannot ever occur as part of the rich tapestry of our unconscious mental lives.
There is, though, an interesting sceptical response. Perhaps what we call our “unconscious thinking” is in fact conscious. There are two ways this could happen. First, perhaps, there is another thinker in me, one who thinks my unconscious thoughts. Second, maybe I have two centers of consciousness. It’s hard to rule out these hypotheses empirically. But they are rather crazy, and all empirical confirmation requires the rejection of crazy hypotheses.