What are Thomas Aquinas's Five Ways, and what is the difference between them and the kalām argument?

This is a fundamental question for understanding one of the most important philosophical contributions to the question of God's existence. Thomas Aquinas (1225-1274), the great Christian philosopher and theologian, presented in his Summa Theologica five ways (quinque viae) to prove God's existence. These ways have profoundly influenced Western philosophy and remain the subject of lively debate today.

The Five Ways in Brief

The First Way: from motion. Everything moved is moved by another. The chain of movers cannot continue to infinity. Therefore there must be a first unmoved mover, and this is what we call God.

The Second Way: from efficient causation. Everything in the world has an efficient cause. Nothing can be the cause of itself. The chain of causes cannot continue to infinity. Therefore there must be a first uncaused cause, and this is God.

The Third Way: from possibility and necessity. We observe things that are possible in existence (they can exist or not exist). If everything were only possible, there would have been a time when nothing existed. But from nothing comes nothing. Therefore there must be a being necessary in itself, and this is God.

The Fourth Way: from degrees of perfection. We observe degrees in things (more good, more beautiful, more true). Degrees presuppose the existence of a maximum degree as a standard. Therefore there exists a being that is absolutely most perfect, and this is God.

The Fifth Way: from finality. Non-rational things regularly act toward ends. What lacks reason cannot tend toward an end except under the direction of a rational being. Therefore there exists an intellect that directs all things toward their ends, and this is God.

The Difference Between Them and the Kalām Argument

The kalām argument (developed by Muslim theologians like al-Ghazālī) focuses on a single issue: the universe cannot be eternal, but must have a beginning, and what has a beginning needs a creator. This is a temporal argument relating to the universe's beginning in time.

Aquinas's ways, however, most of them (especially the first, second, and third) do not depend on the universe having a temporal beginning. Even if we suppose the universe is eternal, these arguments remain valid. They speak about ontological dependence now, not about beginning in the past.

Inadequate Responses to be Avoided

From some defenders:

"These proofs are conclusive and cannot be refuted." This is misleading oversimplification. Aquinas's ways have faced serious philosophical criticism over the centuries (from Hume, Kant, and others). Even contemporary Thomist philosophers acknowledge the need for more precise formulations and responses to objections. Presenting them as final proofs ignores the history of philosophy.

"Whoever denies these arguments denies reason itself." This is an unhelpful exaggeration. Great rationalist philosophers (like Kant) rejected these arguments for complex philosophical reasons, not for denying reason. The disagreement concerns precise philosophical premises, not rationality itself.

From some critics:

"These are medieval arguments, superseded by modern science." This is a historical error. The Five Ways are philosophical, not scientific arguments. They do not speak about physics or biology, but about metaphysical concepts like causation and possibility. Modern science neither "refutes" nor "proves" these arguments, because they operate on a different level.

"The arguments presuppose religious premises in advance, so they are circular." This accusation is imprecise. Aquinas was careful to begin from general observations (motion, causation) that do not presuppose faith. That he calls the conclusion "God" does not make the argument circular, for he explicitly says this is "what people call God," meaning the argument reaches something and then identifies it.

Why These Responses are Inadequate

They share in ignoring the precise philosophical nature of Aquinas's arguments. They are neither "mathematical proofs" that are conclusive, nor "medieval superstitions" that are obsolete. They are philosophical arguments that depend on analyzing fundamental concepts (causation, motion, possibility) and attempt to reach metaphysical conclusions.

Serious Positions in Contemporary Debate

First, contemporary Thomism. Philosophers like Edward Feser and Gaven Kerr defend updated versions of Aquinas's arguments, while responding to objections from Hume and Kant. They insist that a precise understanding of Aristotelian-Thomistic metaphysics shows the strength of these arguments.

Second, the Kantian critique. Kant's followers see that the arguments exceed the limits of reason by applying concepts (like causation) outside the scope of possible experience. One cannot move from observations about the world to conclusions about what is beyond the world.

Third, the contemporary analytic position. Philosophers like Swinburne and Craig present new formulations inspired by the spirit of Aquinas's arguments but with tools of contemporary logic and probability theory. They see that the arguments provide good reasons for favoring theism, even if they are not conclusive proofs.

Fourth, the naturalist position. Philosophers like Graham Oppy analyze the arguments precisely but reject them, claiming that naturalistic explanations are sufficient, or that accepting a "first cause" does not entail accepting the theistic God.

Where We Stand in This Debate Today

The debate over the Five Ways is alive and active in contemporary philosophy. There is no consensus, but there is progress in understanding the subtleties of the arguments and their points of strength and weakness. Even non-believing philosophers often acknowledge that Aquinas's arguments are deeper than they appear and deserve serious study.

The important lesson: these are complex philosophical arguments, not simple slogans. Understanding them requires studying classical metaphysics and patience with precise distinctions. It is not enough to reject them with a sentence or accept them without scrutiny.

For Advanced Reading

─ Intermediate level: Analysis of the First Way (from motion) and its relation to Aristotelian physics
─ Advanced level: The difference between horizontal and vertical chains in causation according to Aquinas
─ Edward Feser, Aquinas: A Beginner's Guide (2009)
─ "Cosmological Arguments" page on our website