Why does a mind seem so unlike any other kind of thing? First, as we just said, minds aren't things — at least they share none of the usual properties of things, like colors, sizes, shapes, or weights. Minds lie beyond the reach of the senses of sound, touch, sight, smell, and taste. Yet though minds aren't things at all, they certainly have vital links to the things we call brains. What is the nature of those bonds? Are minds peculiar entities, possessed alone by brains like ours? Or could those qualities of minds be shared, to various degrees, by everything? Now, when we said, Minds are simply what brains do, that should have made us ask as well, Does every other kind of process also have a corresponding kind of mind? This could lead to an argument. One side might insist that this is merely a matter of degree, because people have well-developed minds while bricks or stones have almost none. Another side might try to draw a sharper boundary, arguing that only people can have minds — and, maybe, certain animals. Which side is right? This isn't a matter of wrong or right, since the issue is not about a fact, but only about when it's wise to use a certain word. Those who wish to reserve the label mind for only certain processes are obliged to specify which processes deserve that name. Those who claim that every kind of process has a corresponding type of mind are obliged to classify all minds and processes. The trouble with this is that we don't yet have adequate ways to classify processes.
Why are processes so hard to classify? In earlier times, we could usually judge machines and processes by how they transformed raw materials into finished products. But it makes no sense to speak of brains as though they manufacture thoughts the way factories make cars. The difference is that brains use processes that change themselves — and this means we cannot separate such processes from the products they produce. In particular, brains make memories, which change the ways we'll subsequently think. The principal activities of brains are making changes in themselves. Because the whole idea of self-modifying processes is new to our experience, we cannot yet trust our commonsense judgments about such matters.
As for brain science, no one ever before tried to study machines with billions of working parts. That would be difficult enough, even if we knew exactly how every part worked, and our present-day technology does not yet allow us to study the brain cells of higher animals while they're actually working and learning. This is partly because those cells are extremely small and sensitive to injury, and partly because they are so crowded together that we have not yet been able to map out their interconnections.
These problems will all be solved once we have better instruments and better theories. In the meantime, the hardest problems we have to face do not come from philosophical questions about whether brains are machines or not. There is not the slightest reason to doubt that brains are anything other than machines with enormous numbers of parts that work in perfect accord with physical laws. As far as anyone can tell, our minds are merely complex processes. The serious problems come from our having had so little experience with machines of such complexity that we are not yet prepared to think effectively about them.