Part 4: The "no magic" theory
I will start my survey of the theories of consciousness with materialism - the "no magic" theory. Materialism is the child of scepticism and a scientific principle called Occam's Razor, which says that of all the plausible theories, the simplest one is prabably correct. "Simplest" here refers to the number of assumptions made by the theory. In the context of consciousness, materialism is often referred to as eliminative materialism, a term associated with Paul and Patricia Churchland.
A true materialist believes that since over the course of millenia, we have found no evidence for the existence of "God", or "souls", or "supreme beings" of any kind, then those things do not exist. The only things that do exist are material - that is, made of matter. Tables are made of matter, and humans are made of matter. There is no reason to assume that consciousness (whatever it is) is not made of matter also. Note that matter in this sense includes energy. In fact, let's use the word "matter" to denote anything that can be detected and measured by physical instruments.
If consiousness is material, then it is located in the brain. That is because you can replace almost every other part of your body without it affecting your consciousness. Well, what are the things we have in our brains? There is the neocortex, which is responsible for building abstractions and interacting with our senses, speech and motor functions. There is the "old brain" - everything that is inside the cortex - which is responsible for things like our instincts. And then there is this strange thing called consciousness that seems to be responsible for making all of our decisions. We cannot detect a "soul"; therefore, it is not there.
According to materialists, such phenomena as belief, intention and love can be explained in terms of physical and chemical processes that occur in the brain. Given enough time, scientific advances will let us understand everything about the basic functions of the brain. Long before that, we will understand completely how simpler organisms work. Take, for example, a virus. There is debate among scientists whether a virus is a living organism. Why is that? It is probably because we already understand a great deal about how a virus operates. A Hepatitis C virus is a tiny ball made up of about 10 different kinds of RNA molecules. We know how it reproduces by infecting living cells. We know most of the chemical reactions that are involved. In some sense, adding a virus to a living cell is no different from adding vinegar to baking soda - there will be a chemical reaction, and we know its outcome. There is nothing special about it. A materialist would say that eventually we will be able to understand humans as well as we understand virii.
The main consequence of this theory is the absence of free will. In short, we are all pieces in a game whose rules are the rules of nature, and our whole life is predetermined from birth to death. All of the decisions that we make have already been made, and our choices in life are merely an illusion. Consiousness is an illusion. Although there are some scientists who try to remain materialistic while side-stepping the issue of free will, it is very difficult to avoid making this conclusion.
Consequently, the main argument against materialism attacks the absense of free will. First of all, people find depressing the suggestion that they have no control over their own life. If that is so, then why should we try? Why not quit our jobs, relax and have fun in life? It's all pre-determined anyway. I think that this line of reasoning is a mistake. So what if free will is an illusion? Since we cannot predict the future, it does not matter that our whole life story has already been written. Since there is no way we can read the story's ending, the fact that free will is an illusion is inconsequential. My decisions clearly have consequences. I'm not jumping out of the window because I know that the outcome will be unfavourable. As far as I can tell, my decisions have consequences, and that is what matters.
So what is the mechanism behind decision-making? Here is a thought. As I have mentioned above, the brain has consciousness (for making decisions), intelligence (for allowing us to operate with abstract concepts) and instincts. What are instincts? First of all, we have the survival instinct. Why do we have it? Simple. Evolution. Any species that didn't have the survival instinct didn't survive very long. Next, we have sexual instincts. Same deal - evolution. I claim (and I'm sure that I'm not the first one to claim) that every desire that you have is the result of some instinct. We have instincts that drive us to try and understand the world around us, instincts to be a good person and make the lives of those around us better, etc. Some of these are the result of evolution, some are imposed by society and family, and some just seem random (different people can have diametrically opposite instincts).
So in the spirit of Occam's razor, here is a dead-simple theory of consciousness. Our large set of instincts defines an extremely complicated "objective function", and every decision that we make in our life is meant to optimise this function. The cortex plays a big role in it because, first of all, it allows us to operate with very vaguely defined instincts in terms of highly abstract concepts. And second of all, it allows us to evaluate the objective function. Remember Jeff Hawkins' memory-prediction framework, where sensory inputs flow up the cortex hierarchy and predictions flow down? Now suppose that you are faced with a decision. Then the cortex can predict what would happen as a result of deciding A and what would happen as a result of deciding B. In both cases, your brain would evaluate the effect on the objective function and choose the better option.
For the mathematically inclined, what I am claiming is that consciousness is the process of optimising an objective function using a brain, where the objective function is given as a complicated weighted combination of our instincts, and the optimization is done using the forward Euler method performed in the neocortex. Obviously, the no free will objection is still valid, but the main afgument for this theory is that it is extremely simple and does not rely on voodoo concepts like "elementary particles of conciousness" and "microtubular bridges between the quantum world and the classical world". Of course, those concepts are fascinating, and I will get to them shortly.