For example, there are probably thousands of different species of trees, but there's something about each particular tree, something we can call "treeness," that all of them share in common and by which we distinguish a tree from, say, a bush. "Treeness" is the universal manifested by particular trees.
Egnor writes that universals - abstract thoughts like treeness, or redness or circularity - are not material yet they exist, but according to materialism everything which exists, including "minds," must be material or at least completely reducible to material stuff. The materialist holds, therefore, that abstract ideas must be the product of a material brain.
Egnor argues that triangularity, the quality of having three straight sides and three angles, would exist even if there were no triangular objects and would exist even if there were no material brains to conceive it.
Here's the nut of his argument:
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.Very well. I'm inclined to agree that universals are real and independent of matter, but I wonder whether it's as easy to demonstrate this as Egnor's argument makes it out to be.
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 fairly clear that realism (whether Platonic, Aristotelian, or Scholastic) is true and that Conceptualism/Nominalism is false. A number of arguments demonstrate this. It seems, 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's 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.
For instance, if universals are independent of matter would universals still exist if there were no universe, i.e. if there were nothing at all. How could anything, even immaterial concepts, exist if nothing existed? In other words, it seems to me that the only way universals could exist apart from a universe containing both matter and human brains would be if they existed in the mind of God.
If so, the realist must presuppose that God exists in order to make the case that universals are independent of matter.
In other words, it seems to be the case that universals exist, but whether they're ontologically distinct from matter and would or could exist if no physical, material stuff existed is not so clear, at least not to me.
If God exists then universals could certainly exist in God's mind. If God doesn't exist then universals would seem to be somehow ontologically dependent upon particular material objects and physical brains, and materialism would thus be correct.
Therefore, the debate between materialism (matter is the only substance) and dualism (mind and matter are two disparate substances), like many philosophical debates, is ultimately a debate between naturalism and theism.
Egnor adds this:
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.If one accepts this argument the conclusion that the human intellect or mind is immaterial pushes one in the direction of theism. If, however, one rejects theism a priori then materialist conceptualism seems to be the most plausible option left.
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.
Why, though, would anyone reject theism a priori?