Here is a handout for one of my classes. Readers here might find it interesting as well. The class read the “Great Debate” on the Secular Web between Andrew Melnyk and the two Christian philosophers Stewart Goetz and Charles Taliafero. This is my explanation of Melnyk’s idea of the physical realization of the mental, which to me is quite plausible.
Mind is defined functionally. A Functional Definition is a definition of something not in terms of its constituents, but in terms of what it does. For instance, since we now have Nooks and Kindles, we would no longer define “book” in terms of being constituted by paper pages and a cloth or paper binder. We would define “book” as “anything that serves to present extended text in a convenient form for reading.” It no longer matters whether a book is composed of processed tree carcasses or of chips and circuits. What matters is what it does.
A functional definition of “mind” would be like a functional definition of “kidney,” where a “kidney” is anything, organic or mechanical, that performs the filtering functions to remove impurities from the blood. A mind is therefore anything, of whatever constitution, that performs the mental functions of thinking, feeling, perceiving, etc. The realizer of a mind would be that thing, whatever it is and however constituted, that performs those mental functions.
According to the theory of the physical realization of the mental, for human beings, the brain is the realizer of all mental functions. In other words, the human brain (or, more accurately, certain subsystems of the human brain) is the human mind because, for humans, it is the brain that performs all mental functions. For human beings, mental activities are a subset of their physical activities.
Since the brain is a physical system then, of course, it performs mental functions physically, i.e. by chemical and electrical causal processes. The brain therefore performs the mental functions in the same general sense that the organs of the alimentary canal perform the digestive functions or that the organs of the respiratory system perform respiratory functions. The brain, in short, is our mental system.
Advantages of the Theory of the Physical Realization of the Mental: Because “mind” is given a functional definition, the problem of multiple realizability does not arise, as it did with the old mind/brain identity theories. A mind is anything that performs mental functions, whether, e.g. it is a human brain, an ET’s brain, or an electronic brain. Further, physical realization solves the problem of mental causation. If mental events are physical performances, then, their causal powers are not mysterious. If noticing that my checking account is low is something that I do with my brain, then it is not mysterious how that awareness (realized as a physical state) causes my next action of deciding to transfer money from my savings account. If mental events just are a kind of physical event, then they can enter into the cause-and-effect nexus just like any other physical events.
Possible Disadvantages: But don’t our mental states have many properties that physical states just cannot have? For instance, cannot a thought be, say, brilliant or humorous? It would be a very odd thing to say that a process in my brain, which is just chemistry and physics, is brilliant or humorous. If thoughts and brain processes have different properties, then they cannot be identical, so the theory of the physical realization of the mental must be false.
But consider an analogy: Singing is a physical process. It is something done entirely with the vocal apparatus, such as the lungs, diaphragm, the larynx, the tongue, etc. Yet we often speak of a particular singing performance, as, say, poignant or enthralling. Of course we would not describe movements of the diaphragm or larynx as poignant or enthralling. A music reviewer and a physiologist would describe a singing performance very differently, but this does not mean that singing is not a purely physical performance. Roughly speaking, the physiologist is concerned with the objective aspects of the singing—how it is physically accomplished. The reviewer is concerned with the subjective aspects of the performance—how it sounds to a listener.
Likewise, we may distinguish between the objective neurological process of thinking and the understood content of the thought. It is essential not to conflate how we think with what we think. How we think is with the physical apparatus of the brain; what we think can be anything. Unsurprisingly, an entirely different vocabulary applies to the intentional objects of our thoughts, such as concepts, ideas, hypotheses, etc. than to the physical process of thinking. For instance, we can think of abstract, non-physical objects such as numbers. We use physical processes to think about non-physical things.* Further, the concepts we employ to understand non-physical things like numbers are very different from the ones we use to understand chemical and electrical processes.
*Why not? Does a driver of fat cattle have to be fat?