What is the Fourth Way (degrees of perfection) according to Aquinas, and why is it considered the most difficult of the Five Ways for contemporary understanding?

The Fourth Way of Aquinas's Five Ways — known as the argument from "degrees of perfection" or "gradation in being" — is perhaps Aquinas's most obscure argument for the contemporary reader. While the other ways (motion, efficient causation, possibility and necessity, teleology) seem translatable into contemporary philosophical language, the Fourth Way appears as if from an entirely different philosophical world. This is not necessarily a flaw in the argument, but rather reflects the metaphysical distance between the thirteenth century and today.

Inadequate responses to avoid

From some defenders of Aquinas:

"The argument is clear: there are degrees in qualities, therefore there is a highest degree, which is God." This is a misleading simplification. The argument depends on complex metaphysics of Platonic participation and formal causality, not merely an observation about the existence of degrees.

"Contemporary criticism of the argument is due to ignorance of classical metaphysics." This accusation avoids the issue. Even philosophers well-versed in Aristotelian-Thomistic metaphysics like Anthony Kenny find the argument problematic. The problem is not mere ignorance.

"The argument works exactly as Aquinas formulated it, needing no modification." This position ignores philosophical development. Even contemporary Thomists like Edward Feser and Eleonore Stump acknowledge the necessity of reformulating the argument to be understandable and convincing today.

And from some critics:

"The argument is a clear fallacy: from the existence of degrees, the existence of a highest degree does not follow." This is superficial criticism. Aquinas does not say that the mere existence of degrees necessitates a highest degree by simple logical necessity, but rather depends on a metaphysical theory about the nature of qualities and participation.

"The argument is purely Platonic, not Aristotelian, so it is foreign to Aquinas's system." This is a historical error. Aquinas integrates specific Platonic elements within an Aristotelian framework, and this is part of his synthetic genius.

Why these responses are inadequate

They share in ignoring the real challenge: the argument depends on a complete metaphysical framework that differs radically from the contemporary framework. Understanding the argument requires first understanding this framework, then evaluating whether the framework itself is convincing.

Aquinas's original formulation

In the Summa Theologiae (I, q.2, a.3), Aquinas formulates the argument with extreme brevity:

"The fourth way is taken from the degrees of perfection found in things. For we find in things something more and less good, true, and noble, and likewise in other perfections. But 'more' and 'less' are said of different things according as they approach in different degrees to something which is greatest... Therefore there exists something which is truest and best and noblest, and consequently most fully in being... Now what is greatest in any genus is the cause of all in that genus, as fire, which is the hottest, is the cause of all hot things... Therefore there exists something which is the cause of being, goodness, and every perfection in all beings, and this we call God."

The logical structure as understood by Thomists

1. Empirical observation: There are degrees of perfections (good, true, noble, being) in things.

2. First metaphysical principle: Degrees are understood by reference to a greater standard ("more" and "less" presuppose "greatest").

3. Second metaphysical principle: What is greatest in any genus is the cause of everything else in that genus (principle of exemplar causality).

4. Conclusion: There exists a being that is greatest in being and perfection, and is the cause of all being and perfections.

Why the argument is difficult for contemporary understanding

First: The concept of "pure perfections"

Aquinas speaks of qualities like "goodness," "truth," and "nobility" as if they were objective perfections capable of gradation. Contemporary philosophy — especially after Hume and Kant — tends to consider these as subjective concepts or human projections. Saying "this is better than that" is understood today as a subjective value judgment, not as an objective metaphysical description.

Second: The theory of Platonic-Aristotelian participation

The argument presupposes that things "participate" in perfections by degrees. This is not merely a metaphor for Aquinas, but a metaphysical theory: finite things possess goodness or being by participating in a higher source. This concept is entirely foreign to modern metaphysics which understands qualities as intrinsic properties of things, not as participations in higher Ideas.

Third: The puzzling fire example

Aquinas's example of fire as "the hottest" and cause of all heat appears today as scientifically incorrect and unconvincing. We know that fire is not the hottest (plasma is hotter), and that heat is not a "thing" that transfers from fire to other things, but kinetic energy of molecules. However, Aquinas uses this as an illustrative example of a metaphysical principle, not as a physical fact.

Fourth: The leap from perfections to being

Aquinas moves from discussing degrees of goodness and truth to degrees of being ("most fully in being"). This presupposes that being itself is capable of gradation — a central idea in Thomistic metaphysics but foreign to contemporary philosophy which considers being as a binary concept (either existing or non-existing).

Contemporary reformulations

Jacques Maritain's attempt: He focuses on perfections that are "unlimited in themselves" such as being, goodness, and truth, versus perfections "limited in themselves" such as being a stone or human. Unlimited perfections when they exist in limited form require an unlimited source.

Edward Feser's attempt: He reformulates the argument through the distinction between essential and accidental properties. Some properties (such as being) are not essential to any finite being, so their existence requires an external source for which this property is essential.

Robert Maydole's attempt: A logical-mathematical formulation based on the principle "for every perfection property, if it is possibly instantiated, there is a being that instantiates it maximally." However, this moves far from the spirit of Aquinas's original argument.

Basic contemporary criticism

Even with reformulations, fundamental problems remain:

1. The problem of relative perfections: Are "goodness" and "beauty" absolute or relative perfections? What is "good" for a lion (hunting a gazelle) is not "good" for the gazelle.

2. The problem of composition: Why must all perfections unite in one being? Why not have one being greatest in goodness and another greatest in power?

3. The problem of exemplar causality: Even if we accept the existence of "the greatest," why must it be a cause of lower degrees? This depends on a very specific theory of causality.

Why the argument remains important

Despite its difficulty, the Fourth Way raises a deep philosophical question: How do we understand the existence of gradation and hierarchy in the world? Why are some things "better" than others in some sense? Even if we reject Aquinas's metaphysical framework, the question remains legitimate.

Some contemporary philosophers (such as Robert Adams in his theory of "divine goodness") attempt to revive Aquinas's basic intuition: that the existence of goodness and beauty in the world points to a transcendent source of these perfections.

Where we stand with this argument today

The Fourth Way remains the most difficult and controversial of the Five Ways. Even among contemporary Thomists, there is no consensus on the best way to formulate or defend it. Most contemporary philosophers of religion — even those supportive of arguments for God's existence — tend to avoid this argument or reformulate it in ways that radically depart from the original.

This does not mean the argument is wrong, but rather that it requires prior acceptance of a metaphysical framework that has become foreign to contemporary thought. In the context of the "rational preponderance" (rajḥān ʿaqlī) method, the Fourth Way perhaps contributes less than the other ways to contemporary cumulative argumentation.

For advanced reading