The argument from degrees, also known as the degrees of perfection argument or the henological argument is an argument for the existence of God first proposed by mediaeval Roman Catholic theologian Thomas Aquinas as one of the five ways to philosophically argue in favour of God's existence in his Summa Theologica. It is based on ontological and theological notions of perfection. Contemporary Thomist scholars are often in disagreement on the metaphysical justification for this proof. According to Edward Feser, the metaphysics involved in the argument has more to do with Aristotle than Plato; hence, while the argument presupposes realism about universals and abstract objects, it would be more accurate to say Aquinas is thinking of Aristotelian realism and not Platonic realism per se.
The fourth proof arises from the degrees that are found in things. For there is found a greater and a less degree of goodness, truth, nobility, and the like. But more or less are terms spoken of various things as they approach in diverse ways toward something that is the greatest, just as in the case of hotter (more hot) that approaches nearer the greatest heat. There exists therefore something that is the truest, best, and most noble, and in consequence, the greatest being. For what are the greatest truths are the greatest beings, as is said in the Metaphysics Bk. II. 2. What moreover is the greatest in its way, in another way is the cause of all things of its own kind (or genus); thus fire, which is the greatest heat, is the cause of all heat, as is said in the same book (cf. Plato and Aristotle). Therefore there exists something that is the cause of the existence of all things and of the goodness and of every perfection whatsoever—and this we call God.
In The One God, Reginald Garrigou-Lagrange offers commentary on this proof. Following is a summary of this commentary.
Summary of argument
The premise of the fourth proof is that “being and its transcendental and analogous properties (unity, truth, goodness, beauty) are susceptible of greater and less.” Thus it is said that some things are more true, more good, etc.
After this premise follows the principle that “More or less are predicated of different things according as they resemble in their different ways something which is the maximum of and which is the cause of the others.” Following is a justification of this principle.
Causal structure of argument
Garrigou-Lagrange notes that it may appear that this fourth way “does not proceed by the way of causality” because it does not follow the same structure as the first three proofs. Unlike the other proofs, it does not explicitly rely on the impossibility of an infinite, essentially ordered causal series. However, in the second article, St. Thomas has already asserted that the only way to prove the existence of God is from his effects, and it is only possible to conduct this proof based on the nature of causality. Therefore, the fourth way is not a probabilistic argument. It does not merely say that because degree is observed in things, it is likely that God exists as an “exemplar in this order” (the order of things that are good, true, and be). Instead, the fourth way proceeds from the necessity of a “supreme Good” as a cause, the “cause of other beings.”
Aquinas explains, “If one of some kind is found as a common note in several objects, this must be because some one cause has brought it about in them.” There cannot be multiple causes for this one note which proceed from the objects themselves. These objects are distinct from each other by nature, and therefore, if they were individual causes, they would produce different effects, rather than the same one effect. Essentially, there must be one nature that produces this common note, rather than each producing it in themselves. Therefore, it is causally impossible for multiple diverse beings to share a common note (goodness, being, or truth) with each as the cause of this note.
By the same principle, “if anything is found to be participated in various degrees by several objects,” the objects which are said to possess more or less perfection cannot contain in themselves the fullness of perfection, or predication of more or less would be meaningless. Consequently, among these imperfect things, the varying degrees of perfection found in them cannot be attributable to themselves. Instead, it must be attributed to some common cause apart from them, since again, if this were not so, a diversity of effects would be observed issuing from the naturally distinct objects, rather than the one participated perfection. It is causally impossible for multiple imperfect objects which participate in perfection to cause this perfection in themselves.
Therefore, there must be one object which possesses this perfection in the highest degree and which is the source of the perfection in the others. Thus, the fourth way “proves the necessity of a maximum in being,” or a Being without a composition of perfection and limited capacity for perfection.
Applications of argument
Garrigou-Lagrange then considers the various ways Aquinas applied this argument to the intellect, truth, goodness, and the natural law.
A syllogistic form collected by Robert J. Schihl follows:
A second syllogistic form:
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