Concept

Universals

Intro

Take two red apples. They share something: their redness. Two triangles share triangularity. Two humans share humanity. These shared somethings (redness, triangularity, humanity, justice, goodness) are called universals. The problem is whether they actually exist out there in any real sense, or whether they are just names we give to similar things.

There are three main answers.

Platonic Realism. Universals exist in their own realm. The Form of Triangle exists whether or not any concrete triangle does. Plato held this; modern mathematical Platonists are close cousins.

Aristotelian and Thomist Moderate Realism. Universals exist in three modes: in God's mind before creation as eternal exemplars, in concrete things as their real shared nature, and in human minds as concepts abstracted from experience. Aquinas runs this view. It is the mainstream Christian metaphysics.

Nominalism. Universals do not exist. Only individual particular things exist; "redness" is just a name (Latin nomen) we give to a bunch of things that happen to be similar. William of Ockham developed this in the late Middle Ages; modern materialism inherits it.

Why does this dry-sounding fight matter? Because Christianity is structurally Realist all the way down. The doctrine that all humans bear the image of God assumes humanity is a real shared nature, not just a label. The doctrine of natural law assumes moral truths are real features of how things are, not human conventions. The doctrine that Christ took on human nature, full stop, requires that there be such a thing as human nature to take on. Nominalism cannot deliver any of these.

This is why arguments like the Stealing from God Argument (Frank Turek) press hard on universals. A worldview that denies that universals are real cannot consistently make universal moral claims, do universal mathematics, or talk about real shared human nature. It is borrowing capital it cannot account for.

In full

The problem of universals, whether abstract properties (justice, redness, humanity, triangularity) exist independently of their instances, is foundational metaphysical infrastructure for classical theism. The three-position trichotomy (Platonic Realism, Aristotelian-Thomist Moderate Realism, Nominalism) underpins at least seven major Christian doctrines and supplies the metaphysical grounding the Stealing from God Argument presupposes. Realism about universals is not optional decoration on the Christian system; it is load-bearing.

The three-position trichotomy

Platonic Realism (universals ante rem only)

Universals exist independently in a separate realm of Forms, prior to and independent of the particulars that instantiate them. The Form of Triangle exists whether or not any concrete triangles do. Plato's classical position; revived in modified forms by some contemporary mathematical Platonists.

Strengths: explains the objectivity, necessity, and intelligibility of universals; underwrites mathematical realism cleanly. Weaknesses: the "third man" regress (if the Form of Man explains what men share, what explains what men and the Form share?); difficulty connecting the Form-realm to the world of particulars; the regress threatens to multiply Forms infinitely.

Aristotelian-Thomist Moderate Realism (universals ante rem, in re, and post rem)

Universals exist in three modes:

Ante rem, in the divine intellect, prior to creation, as the eternal exemplars by which God knows His own essence and creatable possibilities. Aquinas treats divine ideas as God's knowledge of the ways His own essence can be participated in (cf. ST I.15).
In re, in concrete particulars, instantiated in the things themselves. The form of humanity exists in Peter, in Paul, in every human, as a real shared nature.
Post rem, in the human mind, abstracted by the intellect from sensible particulars. We come to know universals by abstraction from instances.

This is the historically dominant Christian view, articulated by Aristotle, refined by Augustine and Boethius, and given its mature form by Aquinas. It avoids the third-man regress (the divine intellect grounds universals without itself being one more universal in need of grounding) and avoids nominalism's deflation (because universals really are in the things, not merely names projected onto them).

Nominalism (universals are mere names or mental constructs)

Only particulars exist. "Humanity," "redness," "triangularity" are at most labels we apply to groupings of particulars that resemble one another, or mental constructs with no mind-independent existence. William of Ockham's via moderna; revived heavily in modernity (Hobbes, Berkeley in some moods, Quine, Goodman, contemporary trope theorists with caveats).

Strengths: ontological parsimony; aligns with empiricist epistemology. Weaknesses: struggles to account for genuine commonality between particulars (why are all triangles triangular if "triangle" is just a label?); cannot ground necessary truths (mathematics, logic); typically presupposes the very universals it denies (concepts of "resemblance," "set," "predicate").

Seven theological applications

The problem of universals is not idle metaphysics. At least seven major Christian doctrines stand or fall on the realist answer.

1. Mathematics grounding

If mathematical objects (numbers, sets, geometrical relations) have no real existence, if "two" is just a label, then the unreasonable effectiveness of mathematics in describing physical reality has no explanation. Theistic moderate realism grounds mathematics in the divine intellect; nominalism owes an account.

2. Moral realism

Objective moral facts ("torturing infants for fun is wrong, in every place and every age") presuppose universal moral truths. The natural intuition, torture-for-fun is wrong simpliciter, not just wrong-here-now-for-me, is the realist position. Nominalism about moral universals is a revisionary commitment that owes a justification, not the obvious starting point. The Moral Argument presupposes moral universals.

3. Trinity coherence

"One essence, three Persons" requires that the divine essence is a real universal, really shared by Father, Son, and Spirit, not merely a label applied to three separate beings (which would be tritheism). The classical incoherence objection ("how can God be both one and three?") conflates the metaphysical categories to which "one" and "three" apply. The Trinity doctrine and its Latin-Thomist coherence defense require realism.

4. Hypostatic union

The doctrine that Christ is one Person in two natures (fully God and fully human) presupposes that "divine nature" and "human nature" are real universals capable of being instantiated in a single Person. The Hypostatic Union is unintelligible under nominalism, there are no real natures for the one Person to instantiate.

5. Original sin and federal headship

Adam's sin imputed to all humanity (Rom 5:12-21) presupposes that "humanity" names a real nature shared by Adam and his descendants, not just a convenient grouping. Federal Headship and Original Sin both depend on the universal being real; if nominalism is true, federal headship collapses into arbitrary divine decree with no metaphysical anchor.

6. Natural law

The doctrine that there are universal moral obligations binding on all human beings as such (not just on those who have explicitly received special revelation) presupposes that "human nature" is a real universal with normative content. Natural Law is a moderate-realist tradition; pure nominalism cannot ground it.

7. The Stealing from God argument

The atheist who affirms objective moral truths, the laws of logic, and the applicability of mathematics to reality is implicitly relying on the existence of universals. Universals require grounding, and the moderate-realist answer (grounded in the divine intellect) is the historically dominant and philosophically robust option. The Stealing from God Argument runs through universals.

The Aristotelian-Thomist resolution

The Moderate Realist position resolves the main objections against both Platonism and Nominalism.

Against Platonism's third-man regress. Anchoring ante rem universals in the divine intellect, rather than in a free-floating, self-subsistent Form-realm, eliminates the regress. God's knowledge of His own essence grounds the universals without generating a further universal in need of grounding. The divine intellect terminates the regress because divine simplicity entails that God's intellect, His being, and His essence are not really distinct (cf. Divine Simplicity).

Against Nominalism's deflation. Positing real shared natures in re, really instantiated in particulars, gives a substantive answer to "why are all triangles triangular." It is not a name-projection; the triangularity is really there, the same in each triangle. The universal is not a separate object floating somewhere; it is the form of the particular thing.

Against modern revisions. Trope theory (universals as bundles of resembling tropes) and resemblance nominalism (similarity is primitive) both face the regress problem differently. To explain why particulars resemble, one must appeal to a respect of resemblance, which is itself a universal property. The Aristotelian framework absorbs trope-theory's intuition (forms-in-things) without paying its ontological price (denying the unity of the form across instances).

Apologetic deployment

The equivocation-defeater pattern (cf. Engaging the Conclusion-Fixed Skeptic) and the Stealing from God Argument pattern both run through universals.

The borrowed-capital move. Atheist objections that appeal to objective morality, the unreasonable effectiveness of mathematics, the intelligibility of science, or the laws of logic have already conceded a metaphysical inventory the atheist's nominalism cannot pay for. The classical theist points out that the universals being relied on require grounding, and the historically dominant grounding answer is theistic (the divine intellect). The atheist either retracts the appeal (and accepts the deflationary cost, moral relativism, mathematical fictionalism, conventionalist logic) or accepts the metaphysical infrastructure that points to theism.

The nominalism-burden move. Nominalism is not the natural starting point against which realism must be argued. The natural intuition, that triangles really share triangularity, that murder is really wrong, is the realist intuition. The nominalist is the one proposing a revisionary metaphysics; the burden of proof is on the revision, not on the default.

Wigner's problem

Eugene Wigner's "The Unreasonable Effectiveness of Mathematics in the Natural Sciences" (1960) remains the standing challenge for mathematical nominalism. If mathematical objects are mere fictions or arbitrary mental constructs, why does mathematics, and especially mathematics developed for purely abstract purposes long before any physical application was foreseen, describe physical reality with extraordinary precision?

The realist has a clean answer: mathematics tracks the structure of reality because the structure of reality is itself mathematical (the laws of nature are the mathematical structure built into things), and that mathematical structure is itself grounded in the divine intellect that is its eternal exemplar. The Wigner phenomenon is exactly what the realist would predict.

The nominalist owes an account that does not reduce to "remarkable coincidence." Quine's later position (mathematics is indispensable to our best scientific theories, so we ought to be ontologically committed to mathematical objects) is itself a partial concession to realism.

Historical sweep

Plato (4th c. BC), Forms in a separate realm; the original realist position.
Aristotle (4th c. BC), Forms in things; the in re mode; the seed of Moderate Realism.
Augustine (4th-5th c.), Forms relocated into the divine intellect; the Christian-theistic ante rem mode.
Boethius (6th c.), preserved the universals problem for the medieval Latin tradition; his commentary on Porphyry framed the medieval debate.
Anselm, Abelard (11th-12th c.), early medieval moderate realism; Abelard's "non-thing universals" foreshadows nominalist moves.
Aquinas (13th c.), the mature Moderate Realism; ante-in-post rem framework; divine ideas doctrine in ST I.15.
Scotus (13th-14th c.), moderate realist with a distinctive doctrine of common nature and haecceitas.
Ockham (14th c.), the via moderna's nominalism; universals are mental concepts, not extra-mental.
Suárez (16th-17th c.), late-scholastic synthesis; influences modern theistic personalism.
Modern era, Hobbes, Locke, Berkeley (variously nominalist or conceptualist); Hegel, McTaggart (idealist universals); Russell, Frege, Quine (the analytic recovery of realism for mathematical purposes); Armstrong, Lewis, Sider (contemporary universalist debates).