C.S. Lewis argued that, if we conceive of rationality and judgments as a physical organ and its products, then we cannot consistently hold that any of our beliefs are rationally explained, as opposed to solely being causally explained.
In reply, some philosophers have suggested that Lewis mistakenly inferred that, if rationality and judgements have a sufficient causal explanation, they must lack a rational explanation. According to these philosophers, Lewis failed to show that rational and causal explanations are incompatible with one another. Insofar as this incompatibility has failed to be established, they conclude, Lewis cannot claim to have shown that naturalism precludes rational explanation.
Can anything be said on Lewis’s behalf? It seems to me that, when we reflect on what a “rational explanation” really amounts to, it can be shown that there is indeed an incompatibility of precisely the sort that Lewis’s argument requires.
One objection that has been raised against Lewis is the claim that “reasons explanations” are distinct, non-causal sorts of explanations that are different from, but not incompatible with, causal explanations. On this view, when we provide reasons for our beliefs, we are not appealing to the causes of our beliefs. Rather, we are placing our belief in the “space of reasons”, where it can stand as reasonable or unreasonable depending on the reasons we cite for holding it. If we can have reasons for belief that are distinct from the causes of those beliefs, it would seem that the existence of sufficient physical causes for our beliefs does not stand in the way of our ability to recognize them as justified on the basis of reasons.
However, the suggestion that reasons provide a special sort of non-causal explanation faces a serious difficulty: If reasons are non-causal in the sense described above, then forming a belief for certain reasons cannot provide any basis for thinking that what we believe is actually true. If I believe that P for some good reason, Q, the truth of my belief will only be guaranteed if Q actually obtains. But if I do not take Q to be what causes my belief that P, then the fact that it is my reason for believing that P does not put me in a position to know whether anything at all ensures the truth of my belief that P. Lewis himself makes a similar point:
“...even if [non-causal] grounds do exist, what have they got to do with the actual occurrence of belief as a psychological event? If it is an event it must be caused. It must in fact be simply one link in a causal chain which stretches back to the beginning and forward to the end of time. How could such a trifle as lack of logical grounds prevent the belief’s occurrence and how could the existence of grounds promote it?” (Lewis 1978, p. 16. Brackets added)
For all I know, Q may be my reason for belief even though, in fact, it is not the case that Q. Consequently, knowing that I believe that P because of some good (non-causal) reason, Q, will not put me in any position to recognize whether my belief is true or false. If reasons are going to serve as explanations that put us in a position to recognize the truth of our beliefs, then they must be facts that cause us to form beliefs as a rational response to what is actually the case.
In light of the considerations above, we should conclude that “reasons explanations” are some sort of causal explanation. If the mind is a physical organ, then reasons must be causes that affect that physical organ in a way that leads to the production of beliefs. However, this proposal is in tension with the claim that we recognize reasons as what cause our beliefs as well as what ensure their truth. In short, we cannot simultaneously hold that the mind is physical and that our beliefs have genuinely rational explanations. If the mind is a physical organ, then the causal relations that obtain between our beliefs and the facts that cause them are determined by the laws of nature that govern our universe. In other words, when certain facts cause a belief to be formed, this will result from the physical character of those facts, the physical character of the mental organ (along with our beliefs), and the laws of nature that determine how things with those physical characteristics interact with one another. However, if this is the case, then there is no basis for supposing that the same facts that cause my beliefs also ensure their truth. Assuming that the mind is a physical organ, is perfectly coherent to suppose that our beliefs are caused by facts that have no relation at all to the things we form beliefs about. Even if it just so happened that our beliefs were caused by facts that ensured their truth, the mere awareness that our beliefs were caused in a certain way would still not enable us to actually arrive at a judgment concerning their truth. In order to recognize our beliefs as true, there must be some evident and essential connection between the causes of our beliefs and the facts that those beliefs are about. But this connection is precisely what we must reject insofar as we hold to the view that the mind is a physical organ. We must reject it because the causes of physical entities are fully determined by their physical characteristics and the laws of nature, not by the intentional content of our beliefs or principles of logical consequence.
We are now in a position to give a precise account of why rational explanations of belief are incompatible with other forms of causal explanation: In order to have genuinely rational explanations that can establish the truth of the beliefs that they explain, there must be an evident and essential connection between the facts that explain our beliefs and the facts that ensure the reality of whatever our beliefs are about. However, as shown above, if the mind is a physical organ that is susceptible to non-rational forms of causal explanation, then there can be no evident and essential connection of this sort. Consequently, insofar as we take our beliefs to have sufficient non-rational explanations, we cannot also hold that they are rationally explained.
Since our beliefs do have rational explanations in terms of reasons that ensure their truth, what should we conclude about the nature of the mind? As this discussion suggests, it cannot be any physical organ. Rather, the reality of reason itself establishes the immateriality of mind and judgment. Insofar as the mind is non-physical, it is not governed by physical laws and the causal relations that they entail. The principles of thought are rational principles that guarantee an essential connection between the causes of our beliefs and their truth. We acknowledge the reality of these principles whenever we recognize the truth of our beliefs in light of the reasons that explain them. The implications of this acknowledgement preclude a purely physical account of the mind and vindicate C.S. Lewis’s belief in a “cardinal difficulty” facing naturalism.
Addendum:
1. It is sometimes suggested that C.S. Lewis’s argument from reason has been improved upon and/or superseded by more sophisticated attempts to show that naturalism is self-defeating. Specifically, Alvin Plantinga’s evolutionary argument against naturalism has occasionally been held up as such an innovation. Without attempting to refute Plantinga’s argument in detail, it is worth highlighting a key advantage of Lewis’s approach: Plantinga’s argument depends upon a controversial premise concerning the prior probability of reliable cognitive faculties, given naturalism and evolution. By contrast, Lewis requires no such assumption. Even if the prior probability of reliable cognitive faculties was high given naturalism and evolution, Lewis’s argument could still succeed. This is because Lewis attacks the very possibility of rational explanations on naturalism rather than their probability.
2. The immaterial mind is governed by rational principles that ensure an essential connection between the explanations of our beliefs and their truth. However, there are clearly cases of false belief and beliefs that are not formed for good reasons. How can the possibility of such cases be explained on this account? Although, in normal conditions, the mind will be caused to form true beliefs for good reasons, exceptional cases of malfunctioning remain possible. When someone forms a false belief or forms a belief without good reasons, these must be explained in terms of a non-rational cause. This will involve some sort of interference, where the mind is acted upon by some external, non-rational cause instead of acting in accordance with its own rational principles. This may seem to present a skeptical threat: If we cannot distinguish between cases in which our mind is acting in accordance with rational principles and cases in which it is being interfered with, how can we be confident that our reasons for some belief actually ensure its truth? The general response to arguments from illusion will also apply in this case. Our inability to recognize when we are reasoning unsuccessfully does not entail that we lack conclusive evidence when we are reasoning well. When we are reasoning well, we know that our beliefs are explained by reasons that ensure their truth. Consequently, even though we are unable to recognize when we are reasoning unsuccessfully, beliefs formed by reasoning well are not subject to doubt.
3. Physicalists may attempt to argue that they can establish a connection between the causes of our beliefs and their truth by appealing to natural selection. Natural selection, they might claim, allows us to account for why our rational faculties successfully track the truth. This may seem to provide grounds for affirming a physicalist account of rational explanation. The difficulty facing any proposal of this sort is simple: These accounts can only explain why our beliefs are generally correlated with the facts that make them true. They do nothing to undermine the key contention that, if the mind is a physical organ, there is no essential connection between the causes and the truth of our beliefs. Furthermore, the absence of this essential connection prevents the physicalist from consistently recognizing the truth of their belief that natural selection favors cognitive reliability in the first place. Because it fails to establish the essential connection required for rational explanation, this evolutionary proposal provides no distinctive advantage for the physicalist.
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