Materialists claim that consciousness is nothing but a product of matter, something that appears in some way from brain activity – just as the kidneys excrete urine, so the brain excretes consciousness.
Not only does such a claim sound very strange on the face of it, but it also has no end to the explanation of how it happens. Of course, it is clear that there is a correlation between brain processes and mental processes, and that influence on one leads to influence on the other.
This has been known since the first man struck his friend's head and caused him to lose consciousness, and the neurosciences have not revealed anything essential here except for the refinement of the subtleties of that correlation. But where does the very consciousness in which those mental processes take place come from? We assume that simple chemicals have no consciousness, and if so how can a certain complex organization of theirs lead to the appearance of something so different from them? It would be similar to the claim that if a sufficiently complex card tower is built, at some point the cards will be able to speak and play on their own.