The natural world can be understood as a hierarchy of entities and their causal powers. Very roughly, we can say that when applying this approach to a human being, at the bottom level of this hierarchy of entities are elementary particles with their causal powers, and at the top, there is the whole human organism. Between these levels, there are a number of intermediate levels such as atoms, molecules, cells and organs. In such hierarchy, the existence of the upper level entities is always (in principle, if not in practice at the current moment) explicable in terms of the existence and operation of the lower-level entities. Similarly, the properties and causal powers of these hierarchically ordered entities can be understood in a way that explains the properties and the causality of the upper-level entities in terms of the lower levels. The resultant picture is one where the bottom-level entities and their properties serve to ultimately explain everything else. The functioning of each level can be explained with reference to the entities on that particular level, and the existence and properties of these entities can be further explained with reference to the lower levels. But the upper levels are not needed to explain the lower levels.
With this picture of the material world in mind, we can now ask the following question: Where can we locate the human mind in such picture? The most obvious answer from the materialist perspective is to identify the mind with the entities and their properties at the level of the whole organism, and in particular, at the level of a particular organ (the brain).
But now we can see a problem. The functioning of a mind cannot override what is determined by the lowest levels of physical entities (such as atoms and subatomic particles). Everything in the system works exactly in the way that these lowest levels make it to work. The mental contents cannot exert a causal influence that would make the atoms behave any differently than they would in the absence of such influence. Now, one may object that this picture fails to take seriously the way that a materialist would view the mind. The materialist might say that such mental properties as one’s belief that something is the case, or one’s consequent intention to act in some particular way in response to that belief, are identical to some collection of particular lower-level physical states in the system, so that the belief and the intention just are those particular states, and surely, one lower-level physical state can cause another lower-level physical state without violating the aforementioned principles of the hierarchy. But this will not solve the problem. The physical level of the hierarchy is supposed to provide a full explanation of the event, and obviously, concepts such as “belief” and “intention” are not part of physics as such. And even if the claim is that such mental properties are “the inside”, so to speak, of the physical phenomenon of the system that is fully described by some ideal perfect physics from “the outside perspective”, it remains the case that it cannot be causally efficacious, given the assumption that it is possible to explain and predict the physical behaviour of the system without reference to the mental. While this might conceivably provide a way to view the mental properties and events as “free-riders” along with the physical system (epiphenomenalism), this does nothing to solve the fundamental problem. For example, it is the case that if I throw a red brick to the window, the property of redness is among the properties of the object that breaks the window, but surely it does not follow that redness is the cause of the window’s breaking. Similarly, this view of the mind has no place for genuine mental causation.
Therefore, it seems that the causal impotence of the mental is almost unavoidable, given the assumptions of thoroughgoing materialism. This conclusion has significant implications. To begin with, such view of the mind has a hard time in explaining why the mind (in the sense of the contents of one’s conscious experience, acts of conscious will, etc.) should exist at all. Given that the mental contributes nothing to the physical functioning of the organism, one would not expect it to exist at all, were it not for the fact that one will unavoidably begin with the premise that the mental does exist, based on one’s immediate access to his/her own conscious mental life. (Perhaps one may understand this point more easily with a thought-experiment about a scientist that observes the behaviour of a highly complex robot that is comparable to human beings in its behaviour. One would naturally want to know about not just the causal relationships between the physical parts, but also about whether or not it has a conscious life.)
The evolution of the mental is something that must be seen as very improbable on the basis of the foundational premise of materialism. But even more importantly, assuming (as we inevitably do) that the mental does exist, it should be clear that we have no reason at all to trust on the reliability of the mental contents (beliefs about the external world, etc.) on the assumption that the mental is causally impotent. For every belief, there is one way (in an absolute sense) or a small range of various ways (in an approximate sense) for it to be true, in comparison to the potentially infinite number of ways that it can be false. And being causally impotent, the truth-conducive belief-forming mechanism cannot have evolutionary advantage over ones that produce false beliefs. After all, natural selection can only select an organism on the basis of its behaviour and physical properties (neither of which are affected by the mental if it is causally impotent). If, on the other hand, we take the personal as more foundational than the material, this opens up new possibilities that can solve the problems that were just pointed out. The personal can contain properties that are not reducible to the material (such as causal powers that are in some ways independent of the causal powers of the material constituents of one’s body – even though such powers are in a tight relationship to the material), and also, the mind-body relationship of a human being can be understood in fundamentally teleological terms as something that has been brought about by design (though this does not negate the reality of the relevant natural causes).