The debate between those who believe that everything is reducible to material substance and those who believe that there's more to reality, especially the human being, than just matter is one of the most interesting of the perennial controversies in philosophy. It goes back at least to the ancient Greeks and has popped up repeatedly throughout the history of Western philosophy.
In 1714 Gottfried Leibniz, one of the greatest philosophers and mathematicians in history invited us to consider an interesting thought experiment that he, and many others, believed shows the inadequacy of physicalism (i.e. the belief that everything is explicable in terms of purely physical or mechanical processes):
Suppose that there be a machine, the structure of which produces thinking, feeling, and perceiving; imagine this machine enlarged but preserving the same proportions, so that you could enter it as if it were a mill. This being supposed you might visit its inside; but what would you observe there? Nothing but parts which push and move each other, and never anything which could explain perception.
The machine, of course, is analogous to the brain. If we were able to walk into the brain as if it were a factory, what would we find there other than electrochemical reactions taking place along the neurons? How do these chemical and electrical phenomena map, or translate, to sensations like red or sweet? Where, exactly, are these sensations? How do chemical reactions generate things like beliefs, doubts, regrets, certainty, or purposes? How do they create understanding of a problem or appreciation of something like beauty? How does a flow of ions or the coupling of molecules impose a meaning on a page of text? How can a chemical process or an electrical potential have content or be about something?
Regarding the first question in the preceding paragraph, consider another thought experiment, this one a paraphrase of one authored by philosopher Frank Jackson:
There is a distant planet in which there are no colors except shades of black and white. A brilliant scientist who has lived his entire life on that planet has spent his career receiving radio transmissions from colleagues on earth explaining to him the chemistry and physics of color and what it does to the neurochemistry of the brain so that the scientist knows everything there is to know about the color red. One day he has the opportunity to come to earth where he finds himself surrounded by colors as he disembarks from his spaceship. As he looks around would he be able to identify red or distinguish it from blue? Would there still be something about red that he doesn't know, namely, what it looks like?
The point is that you can know everything about the physical characteristics of a phenomena, you can know what effects are triggered by certain wavelengths of energy in your brain, but still not know what red actually is. An exhaustive physicalist description of red is still incomplete. It does not tell us everything there is to know about red. This suggests that no amount of physical understanding of the material brain can account for qualia, i.e. the sensations we experience by virtue of the functioning of our senses. There is, therefore, good reason to think that there is more to our conscious experience than just the workings of the brain.
If you believe you have a mind (or a soul) nothing in the materialist point of view should intimidate you into giving that belief up.
RLC
