Two crucial components of this picture of human knowledge are the theses that concepts are irreducible to sensations and mental images, but can nevertheless be abstracted from imagery by the intellect. As I have discussed before, a key difference between the Aristotelian-Thomistic position on the one hand and early modern forms of rationalism and empiricism on the other is that each of the latter kept one of these Aristotelian-Thomistic theses while rejecting the other. Rationalism maintained the thesis that concepts are irreducible to sensations and mental images, but concluded that many or all concepts therefore could not in any way be derived from them. Hence, rationalists concluded, many or all concepts must be innate. Modern empiricism held on to the thesis that concepts derive from mental imagery, but concluded that they must not really be distinct from them. Hence the modern empiricist tendency toward “imagism,” the view that a concept just is an image (or an image together with a general term).
These fateful moves are key to understanding the later trajectories of the rationalist and empiricist traditions. The notion of innate ideas gave rationalism confidence that it had the conceptual and epistemic wherewithal to ground an ambitious metaphysics. But rationalist metaphysical systems can be so bizarre and revisionary that they are open to the objection that their lack of an empirical foundation leads them to float free of objective reality. Modern empiricism, by contrast, has usually been much more metaphysically modest. But it has also had a tendency to be too modest, to the point of collapsing into skepticism even about the world of common sense and ordinary experience. Here the critic can charge that collapsing concepts into imagery has prevented modern empiricism from being able to account for any knowledge beyond the here and now.
Now, both approaches can be and have been modified by various thinkers in ways that seek to avoid problems like those mentioned – though from the Thomistic point of view, only a return to the broadly Aristotelian conception of knowledge from which they each in their own ways departed can afford a sure remedy.
But general epistemology is not my concern here. What I want to do instead is note two general approaches to natural theology that might loosely be labeled “rationalist” and “empiricist,” even if their practitioners don’t necessarily all self-identify as such. They are approaches that are, from the Thomist point of view, deficient in something analogous to the ways in which rationalist and modern empiricist epistemology and metaphysics in general are deficient. And like those views, they represent opposite vicious extremes between which, naturally, Thomism stands as the sober middle ground.
On the one hand we have an approach that aims to establish admirably ambitious traditional metaphysical conclusions – such as the existence of God and the immortality of the soul – by way of an essentially rationalist methodology. One example would be Plantinga’s ontological argument for God’s existence, and another would be Swinburne’s conceivability argument for dualism. Plantinga’s argument proceeds by considering what might or must be the case in various possible worlds, and on that basis aims to establish the existence of God in the actual world. Swinburne’s argument begins with what we can conceive about the mind, and draws the conclusion that its essence or nature must be of an immaterial kind.
From the Aristotelian-Thomistic point of view, both these arguments get things precisely backwards. We don’t start with possibilities and then reason from them to actualities. Rather, we start with actual things, determine their essences, and then from there deduce what is or is not possible for them. We don’t start with what we can conceive and then determine a thing’s essence from that. Rather, we start with a knowledge of its essence and then determine, from that, what is actually conceivable with respect to it, and what merely falsely seems to be conceivable.
From the Thomist point of view, while the metaphysical conclusions of such arguments are not too ambitious, the method for arriving at them is. We cannot do so entirely a priori. To be sure, once we do establish the existence of God (through arguments of the kind I’ve defended at length elsewhere), we discover that he is such that, were we fully to know his essence, we would see that his existence follows from it of necessity, just as the ontological argument claims. But what we can’t do is jump directly to such an argument as a standalone proof of his existence. Similarly, when we first establish that the intellect is by nature immaterial, we will see that it is indeed conceivable for it to exist independently of the body (topics I’ve dealt with e.g. here and here). But in that case the appeal to conceivability is rendered otiose as grounds for establishing the intellect’s immateriality.
On the other hand, we have arguments that proceed a posteriori, but are way too unambitious in their conclusions. This would include, for example, arguments that treat God’s existence as at best the most probable “hypothesis” among others that might account for such-and-such empirical evidence, or even fail to get to God, strictly speaking, as opposed to a “designer” of some possibly finite sort. And it would include arguments for survival of death that put the primary emphasis on out-of-body experiences and other phenomena that can at best render a probabilistic judgment.
Thomists tend to put little or no stock in such “god of the gaps” and “soul of the gaps” arguments. At best they are distractions from the more powerful arguments of traditional metaphysics, and thus can make the grounds for natural theology seem weaker than they really are. At worst, they can promote serious misunderstandings of the nature of the soul, of God, and of his relationship to the world. (For example, they can give the impression that it is at least possible in principle that the world might exist without God, which entails deism at best rather than theism. And they can give the impression that the disembodied soul is a kind of spatially located or even ghost-like thing.)
For the Thomist, the correct middle ground position is to hold that the soul’s immateriality and immortality, and the existence and nature of God as understood within classical theism, can all be demonstrated via compelling philosophical arguments, but that the epistemology underlying these arguments is of the Aristotelian rather than rationalist sort. (Again, I defend such arguments for the existence and nature of God in Five Proofs of the Existence of God, and have argued for the immateriality and immortality of the soul here and here. Much more on the latter topics to come in the book on the soul that I am currently working on.)