In order to refute the notion that sympathizing with psychiatry or being a psychiatrist necessarily entails that one believes that the human consists of nothing but matter, let us look at the different philosophical views on the metaphysics of reality in general, and the human person in particular. Many accuse psychiatrists of teaching that the only kind of substance that exists is matter; a view called 'materialism.' From this perspective, even human experience is totally reducible to certain configurations of matter.
We will refer to materialism as "physicalism." This is the thesis that everything is either made of matter, necessitated by, or supervenes upon, the physical. The label "physicalism" was introduced by Otto Neurath and Rudolf Carnap; logical positivist philosophers who believed that knowledge could only be acquired through empirical verification. Indeed, the metaphysical position of physicalism is very often associated with the epistemological position of empiricism.
Stoljar (2009) points out that more contemporary physicalism emphasizes continuity with the physical sciences, which admits of entities distinct from concrete extension, such as gravity, for example. The physicalist is more concerned with the immanent realm of spatiotemporal reality being the only meaningful realm of which one can speak, as opposed to a transcendent spirit realm, than of affirming concrete, palpable substance.
Essential to the modern concept of physicalism is the concept of supervenience. David Lewis' explanation of the concept of supervenience is very helpful:
"A dot-matrix picture has global properties — it is symmetrical, it is cluttered, and whatnot — and yet all there is to the picture is dots and non-dots at each point of the matrix. The global properties are nothing but patterns in the dots. They supervene: no two pictures could differ in their global properties without differing, somewhere, in whether there is or there isn't a dot" (1986, p. 14).
In this case, mind supervenes upon matter such that nothing can "differ" with respect to matter without also differing with respect to the mind. The philosophical slogan for this notion is, "there cannot be an A-difference [in this case, a difference in brain matter] without a B-difference [in this case, a subsequent difference in the mind]"(McLaughlin & Bennett, 2014).
In this very bare and minimal 'supervenient' sense, it is a wonder that there is anything controversial about the notion of physicalism with respect to the spatiotemporal realm. "The basic idea is that the physical features of the world are like the dots in the picture, and the psychological or biological or social features of this world are like the global properties of the picture"(Stoljar, 2009). As Stoljar points out, on this picture, the world is simply a pattern of dots, and the psychological and social features of the world are simply distinct patterns within this pattern.
For everything to supervene on the physical, however, does not necessarily mean that everything is reducible to the physical. We will see this more clearly later on, when we talk about the concept of emergent properties. Indeed, I will argue that Thomas Aquinas provides a very helpful metaphysical and philosophical anthropology for those of us who take the material constituents of mankind seriously, yet want to avoid a reductive physicalism.
If we are to take a Lewisian twist on the more abstract notion of supervenience, mentioned earlier, that there can be no A-difference without there being a B-difference, we might say, as Stoljar points out, that "no two pictures can be identical in the arrangement of dots but different in their global properties"(Stoljar, 2009). "Similarly, one might say that, in the case of physicalism, no two possible worlds can be identical in their physical propeties, but differ, somewhere, in their mental, social or biological properties"(Stoljar, 2009). For physicalism to be true in the actual world, as Stoljar points out, means that no other possible world can differ from it physically while being different from our actual world in another respect.
Stoljar formally summarizes this understanding of physicalism: "Physicalism is true at a possible world w iff any world which is a physical duplicate of w is a duplicate of w simpliciter"(Stoljar, 2009). This definition of physicalism is one way of answering the question of what it means to say that everything is physical. What physicalism means, isn this instance, "is that if physicalism is true, there is no possible world wich is identical to the actual world in every physical respect but which is not identical to it in a biological or social or psychological respect"(Stoljar, 2009). Stoljar refers to this understanding of physicalism as "supervenience physicalism"(Stoljar, 2009).
Physicalism, as a belief system, is frequently repudiated by those engaged in philosophy of mind, particularly when it comes to discussion of the relation of qualia to the brain, mind and consciousness. It is clear from such discussions that a secular worldview does not at all necessitate a reductive physicalist view of the human being.
Indeed, there is a great deal of diversity among physicalists when it comes to specific debates within philosophy of mind. What all physicalists have in common, however, is a commitment to so-called "supervenience" physicalism, or, following David Lewis, "minimal" physicalism. It ought to be noted, however, that "physicalism" in the philosophy of mind is sometimes understood as referring to the identity theory, such that mental states are equated with physical states. This, however, is a much narrower usage of the term.
Supervenience becomes a particularly important concept for our purpose, since it is one of the most important concepts in articulating what is known as a non-reductive physicalism. That is, just because mind supervenes upon matter, does not mean that mind is equivalent to matter or ultimately reducible to matter. Matter may be necessary for the spatiotemporal human, but the mind is not therefore equal to it. It is, to use philosophical language, irreducible and metaphysically primitive.
McLaughlin, Brian and Bennett, Karen, "Supervenience", The Stanford Encyclopedia of Philosophy (Spring 2014 Edition), Edward N. Zalta (ed.), URL = <plato.stanford.edu/archives/spr2014/entries/supervenience/>.
Stoljar, Daniel, "Physicalism", The Stanford Encyclopedia of Philosophy (Fall 2009 Edition), Edward N. Zalta (ed.), URL = <plato.stanford.edu/archives/fall2009/entries/physicalism/>.
Lewis, D., 1986, On the Plurality of Worlds, Oxford: Blackwell.