Materialism asserts that all aspects of the mind, including abstract thought, are material in nature. The classical hylemorphic model of the mind — as championed by Aristotle and his interpreters — asserts that some aspects of the mind, such as the intellect, are immaterial in nature. This question about the material/immaterial nature of abstract thought is crucial to the debate over the plausibility of materialism. How can an abstract thought be wholly the product of brain matter? The materialist argues (implausibly) that it can. The dualist argues that it can’t .

To understand the debate, it is helpful to consider the types of abstract objects of thought.^*

The most obvious abstract kind of thought is thought about universals. Universals are patterns that particular objects in nature share in common. Particular objects include a red rose, a red fire truck, a red sunset, and a red dress. “Redness” is the universal that these particular red objects share in common. This “redness” is abstract: there is no particular object that is “redness” itself. Redness itself can’t be localized. It has no dimensions and no particularity. Yet it clearly exists: we can speak of it easily. I can talk about redness and you know just what I mean.

As a universal, which is a pattern or quality shared by some particular object, redness is abstract. It is abstracted from particular things by your mind when you imagine red things.

So what is a universal? There are four general ways that philosophers have tried to explain universals, and they may be termed Platonism, Aristotelianism, Conceptualism , and Scholasticism. Platonism, Aristotelianism, and Scholasticism assert that universals are real, in one sense or another. Conceptualism asserts that universals exist only as constructs of the mind, and have no existence outside of the mind. Platonism, Aristotelianism, and Scholasticism are realist/dualist views of nature, and are consistent with a dualist view of the mind. Conceptualism, while not requiring a materialist perspective, is consistent with materialism and is the understanding of universals generally (and necessarily) taken by materialists.

Platonism, following Plato but developed in greater depth by the Platonists of the early first millennium AD, is the view that universals exist in a pure realm of Forms, and that we intuit copies of these Forms in the natural world. Platonic realism has a number of well-known problems (including problems of infinite regress: is the theory of Forms a Form? is the theory that Forms are a Form, a Form?).

Aristotelianism is the view that universals exist in particular objects, not in a separate realm, and are abstracted from the particular object by the active intellect when the universal is contemplated.

Scholasticism is in some sense a synthesis of the Platonic and Aristotelian views: it is the view that universals exist first in the Mind of God, and are instantiated in particular created objects and are abstracted by the mind by the active intellect.

Conceptualism is the denial that universals have any real existence apart from concepts in the mind. It is derived from Ockham’s theory of Nominalism, which is the assertion that universals are merely names we give to categories of particular objects, but that universals themselves have no real existence at all.

It seems clear that realism (whether Platonic, Aristotelian, or Scholastic) is true and that Conceptualism/Nominalism is false. A number of arguments demonstrate this. It is clear, for example, that “triangularity” doesn’t exist wholly in any particular object. Nothing in the real world is “triangularity,” in the sense that nothing has three closed perfectly straight sides with internal angles summing exactly to 180 degrees. All real triangles are imperfect instantiations of triangularity, yet triangularity is something real in a meaningful sense. We are talking about it, and if we and all triangular objects ceased to exist, triangularity — closed three straight-sidedness with 180 degrees interior angles — would still be a thing.

Triangularity is more than merely conceptual; it real in a meaningful sense, independent of the mind, and it is not perfectly instantiated in any particular object.

Realism is the only coherent view of universals. Universals are real, and not merely mental constructs.

So how is it that the reality of universals demonstrates the immateriality of the human intellect? Since universals cannot exist wholly in particular things, universals as objects of thought can’t exist wholly in brain matter. A “concept of a universal” — a concept of redness or triangularity or whatever — must be an immaterial concept, because a universal cannot be a particular thing. Particular things can be instances of a universal, but the universal itself, and any concept of it, is immaterial. Abstract thought, such as thought of universals, is inherently immaterial. Materialism fails to account for concepts that abstract from particular things.

Materialism itself is an abstract concept. Ironically, materialism fails to account for how it is possible to believe in materialism.

*  For this discussion, I am indebted to Ed Feser and his superb new book Five Proofs of the Existence of God. Feser provides a detailed, lucid examination of five classical demonstrations of God’s existence — not the famous Quinque Viae of St. Thomas, but five different proofs championed by Aristotle, Plato, Augustine, Thomas, and Leibnitz. Feser provides an in-depth discussion of many of the philosophical implications of materialist and dualist understandings of nature, so the book is valuable for its metaphysical, as well as theological, insight.

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