A question that people have been asking since the dawn of cognition is how exactly it is that we can think. Many cultures throughout history have believed that the body is controlled by an immaterial soul or spirit, and that this soul continues living after the death of the body. Some of these cultures believe that the soul is reincarnated afterward. The ancient Egyptians believed that the heart was where thinking occurred, and the brain was a useless muscle. Even today, this belief persists in the form of figures of speech, such as talking about what your heart tells you, or telling someone to have a heart. At some point, however, possibly in ancient Greece, philosophers noticed that people acted differently after receiving a head injury. Modern understanding confirms this, because the brain has been fairly conclusively shown to be the thought center of the body. Our every action is the result of the flow of information through our brain cells (neurons). So what does this mean for thought itself?
Let's do a thought experiment (ah, sorry, no pun intended) commonly referred to as the "China brain" experiment. For the sake of argument, let's say that there are as many people in China as there are neurons in the human brain. (This would be somewhere around 100 billion, but work with me here.) Now, let's also say that, for whatever reason, each of these people is tasked with simulating the action of neurons. Using radios, computers, and so on to communicate with each other, they simulate the flow of information from neuron to neuron just as it happens in a human brain. If some of these people simulated visual input from simulated eyes, the information would flow as in a human brain. The question is this: Does this brain form a consciousness?
A lot of people are very divided on this question. Some say that the very notion is absurd, and that there wouldn't be a soul or some sort of "brain field" that formed from these people getting together and pretending to be a brain. Others say that it only seems absurd because we're not used to thinking about brains made of anything other than actual neurons, and since the input/output of the system would be the same as a "real" brain, it would have to be considered conscious. Part of the problem lies in different definitions of consciousness. Both sides of the issue probably wouldn't consider a calculator conscious, and they probably wouldn't consider a goldfish conscious, and for both of them, a great ape or a dolphin might be sort of a gray area, but the difference is shown by the inability to agree on whether or not this hypothetical China could be conscious. And of course there are many other arguments in between.
Let's do another thought experiment. Suppose that there was a person who looked exactly like you. This person also had a brain, just like you, and reacted to everything the way you would. If you asked it a question, it would respond the same way you would. If it was sitting around and had nothing to do, it would go on Whyville and read the Times. Also suppose that this person isn't conscious. Could this be so?
This concept is called the "philosophical zombie," and it also shows differences in how people think of consciousness. As in the first question, some would say that such a being could exist, and just acting like a conscious person doesn't make someone conscious, and others would say that the very appearance and assertion of consciousness does, in fact, make something conscious.
Of course, if you're going to consider the thought process as only coming from the neurons in your brain, that raises the question of how much "you" actually control. Is there some sort of conscious entity that is "you" that is controlling which way the energy flow of your neurons goes? If so, how does that "you" think? Yet, without this "you," it seems less and less likely that we have free will or can truly make decisions.
Maybe you're wondering why this all matters. "Whether or not we have free will," you might say, "doesn't really matter. If we are conscious and can decide things for ourselves, then there's no point in deciding we aren't and can't. And if we aren't conscious or don't have free will, then it's not really up to us, is it? So why worry?" This is a fair point, but this question is perhaps more relevant now than it ever has been before. With the computer technology and capacity we have now, it seems possible that we may someday create artificial intelligence, which, if you're one of the people who thought that the China brain could think, is indistinguishable from "real" intelligence.
All this is important because it could affect how we treat such systems. Will we treat them as servants or slaves, like we do to calculators? Or will we treat them as equals, albeit with different types of mental configurations? George Johnson said in 1986 that "Using an equivalent set of tokens and rules, we can do thinking with a digital computer, just as we can play chess using cups, salt and pepper shakers, knives, forks, and spoons." He considered the only difference between identically programmed human and computer brains to be the format on which they existed, as with the difference between music on tape or CD. Edsger W. Dijkstra compared the issue of computer thought to simple word choice, "The question of whether a computer can think is no more interesting than the question of whether a submarine can swim." Alan Turing, who helped invent modern computers as we know them, thought that computers could be as conscious as we are, and devised the "Turing test" to determine if a program can think, in which a judge communicates via chat program with either a person or program and must decide which they're talking to. There can also be other input, such as interpreting sounds and shapes. So far, no program has successfully passed the test.
At this point, you may be wondering what I think. I don't think that souls exist, because they don't really account for the direct link between brain state and mental functioning, but at the same time I can't really let go of the notion of free will, either. Basically, I don't know. But I'm certainly interested.
Author's Note: Sources and further reading: