Victor Reppert and I have been arguing for forty years. Our first debates took place when we were both students at Candler School of Theology, Emory University way back in the seventies. For a while, we even lived down the hall from each other in the same house. (Among other things, I learned that you do not play chess with Victor unless you do not mind losing.) Our exchanges have continued in public and in private ever since. While I have learned a lot, I remain frustrated. There are some basic points about which we not only still disagree, which is to be expected, but where the basis of our disagreement is not really clear—not to me at least. Perhaps one or both of us is invincibly ignorant on some points, but I hope not, and on the basis of that hope I will try to get the bottom of one point.

One point of intractable disagreement concerns the mental and the physical. I maintain that some physical acts are mental acts. That is, I hold that human mental acts are fully realized in the physical functioning of the human brain. As I see it, “mental” and “physical” are not names of disparate ontological categories but are related as performance to performer. An analogy would be the relation of a song to a singer. A song is not a physical thing, but an abstract pattern of sounds and words that can be physically realized in the performance of a singer. When Renée Fleming sings an aria, no one questions that the performance is a purely physical one, accomplished by her lungs, diaphragm, larynx, and other parts of her vocal anatomy. Yet the performance is a physical realization of something not physical. Again, the aria itself, as an intellectual creation of a composer and a librettist, is not a physical thing but a pattern capable of indefinitely many distinct representations and realizations.

I suggest that, similarly, the best way to understand something like Einstein thinking “E = mc²” is that in thinking that thought Einstein was executing a performance, analogous to singing an aria, in which the comprehension of an abstract conceptual content (a mental act) was something he did with his brain. In general, the “mental” is something the physical does, and so a “mind” should be understood functionally as anything that performs mental acts. By the way, though I think that “mind” should be defined functionally, I am not a “functionalist.” Functionalism defines mental states in relational terms, but I see this as fundamentally wrong. It seems to me that many mental states must be defined in intrinsically and irreducibly qualitative and non-relational terms. Therefore, as I see it, qualitative mental states, such as a perception of redness, are creations of the brain, and qualitative terms like “red” or “sweet” are properly understood, not in relational terms, but as adverbial modifications of the nature of our conscious experience. It is more accurate to say that we see “redly” rather than that we “see red,” which misleadingly implies that a qualitative modification of an experiential process is an object or thing.

Victor finds such suggestions incoherent, but I have not yet succeeded in finding out exactly why. Often our discussion comes down to whether a brain can understand logic. Note that the question is not whether a physical system can do logic. Obviously, you can easily program the syntactic rules of, say, propositional logic into a computer. Likewise, the standard functionalist types of explanation could surely account for the fact that brains can do logic problems and proofs. However, Victor would maintain that not only can we do logic, but we can understand what we are doing. We have knowledge of semantics as well as syntax. Maybe then, for the sake of argument, we should concede the point of arguments like Searle’s Chinese Room that machines might simulate human understanding but cannot duplicate it. Victor holds that neither computers, brains, or any other physical system can genuinely understand. Let me see if I can capture his reasons why.

Victor often notes that a brain, as a physical system, operates in accordance with the laws of physics. Presumably, nothing miraculous occurs in the operation of the brain. Like any other complex physical system, a rainforest perhaps, nothing occurs at any level that is not, at rock bottom, a causal consequence of the operation of microphysical entities, behaving in accordance with their nature, that is, in accordance with the laws of physics. The laws of logic, on the other hand, are expressions of abstract relations between ideational contents. Such laws are of a fundamentally different sort from the laws of physics in that they entail nothing about the behavior or physical bodies. True, we sometimes think logically (far too often not), but even when we do we do not have to.

By contrast, if we can exclude quantum effects, a brain is supposedly a deterministic system with its total state in a given moment being determined by its total prior state plus any external causal input delivered by the senses. In other words, what makes the brain do what it does comes down to physical causality and if, as naturalists hold, the laws of logic, qua nonphysical, have no causal efficacy, then they cannot determine and brain processes. If, as naturalists hold, brain process determines mental process, then the laws of logic can have no efficacy in determining our mental acts. For instance, when we reach a conclusion, we cannot explain that we reached the conclusion logically, or due to the laws of logic. On the contrary, impersonal, non-rational, and non-normative physical processes determined that outcome. Logic had nothing to do with it.

I hope that the above paragraph accurately captures Victor’s reasoning. Again, my reply would be that, indeed, the “laws of logic” are abstract conceptual or propositional contents and relations, and per se have no causal efficacy. However, I maintain that the act of grasping or comprehending those abstract contents and relations is a physical act, a performance of the brain, and that act, qua physical most definitely does enter into the nexus of physical causation. In that sense reasons are causes. It is not the abstract propositional content of, say, the statement of modus tollens that constrains or compels me to reason in accordance with that rule, but rather my physical act of recognition that modus tollens is a valid argument form that, in complex combination with other causal factors and conditions, determines my conclusion in accordance with that rule.

So, if Victor, or anyone, can tell me—clearly and cogently—why understanding logic or anything else is something that brains cannot do, I would be most appreciative.