Cosmological Argument Aquinas

Overview and Historical Context

The cosmological argument in the thought of Thomas Aquinas (1225–1274) is a central component of medieval natural theology. It aims to show, using reason alone, that there must be a first cause or necessary being explaining why anything exists or changes at all. Aquinas developed these arguments in dialogue with Aristotelian metaphysics and earlier Christian, Jewish, and Islamic philosophers, such as Avicenna and Maimonides.

In the Summa Theologiae (I, q.2, a.3), Aquinas famously presents Five Ways (quinque viae) of demonstrating God’s existence. Three of these—based on motion, efficient causation, and contingency—are usually classified as cosmological arguments, since they reason from general features of the cosmos (change, causation, existence of contingent beings) to a transcendent explanatory ground.

Aquinas does not seek to prove that the universe had a temporal beginning; in fact, he holds that reason alone cannot decide whether the world is eternal. His cosmological arguments are instead metaphysical: even if the world had existed eternally, he argues, it would still require a here-and-now explanation in terms of a necessary first cause.

Aquinas’s Cosmological Arguments

Aquinas offers several related forms of the cosmological argument. The three most central are the First Way (from motion), the Second Way (from efficient causation), and the Third Way (from contingency and necessity).

The First Way: From Motion (Change)

1. Observation of motion: Things in the world are in motion, where motion broadly means change (from potentiality to actuality), not just spatial movement.
2. Principle of causality of motion: Whatever is moved is moved by another; nothing can be in the same respect both potential and actual, so it cannot actualize itself.
3. Rejection of infinite regress (in an essentially ordered series): An infinite regress of movers, where each depends here-and-now on a prior mover, would leave no actual source of motion.
4. Conclusion: Therefore, there must be a first unmoved mover, which initiates motion without itself being moved.

Aquinas identifies this first unmoved mover with God, understood as pure actuality (actus purus) without unrealized potential.

The Second Way: From Efficient Causation

1. Observation of efficient causes: In the world, we encounter an ordered series of efficient causes (causes that bring things into existence or change).
2. No self-causation: Nothing can be the efficient cause of itself, as this would imply existence prior to itself.
3. Rejection of infinite regress (essentially ordered causes): In a hierarchical series where each cause derives its causal power from another in the present (e.g., a hand moving a stick moving a stone), an infinite regress would mean no source of causal power exists.
4. Conclusion: Hence, there must be a first efficient cause that causes without being caused.

Again, Aquinas identifies this first efficient cause with God. Importantly, the relevant regress is not merely temporal but hierarchical and simultaneous: he is rejecting an infinite chain of causes whose power is derivative all the way down.

The Third Way: From Contingency and Necessity

1. Existence of contingent beings: Many things in the world are contingent; they come into being and pass away, and they might not have existed.
2. Possibility of non-existence: If everything were contingent, then there would be a time when nothing existed.
3. Ex nihilo nihil fit: If at some time nothing existed, then nothing would exist now, because nothing comes from nothing.
4. Therefore, not all beings are contingent: There must be at least one necessary being that cannot not exist.
5. Explanation of necessary beings: Some necessary beings might have their necessity caused by another; to avoid an explanatory regress, there must be a being that is necessary in itself, not derived from another.
6. Conclusion: This ultimately necessary being is what Aquinas calls God.

This argument relies on a distinction between contingent and necessary existence and on the idea that the totality of contingent beings cannot be self-explanatory.

Philosophical Significance and Criticisms

Aquinas’s cosmological arguments have been highly influential in both scholastic and contemporary philosophy of religion, shaping discussions about metaphysical explanation, causal principles, and the nature of necessary existence.

Supporters argue that:

• The arguments reveal a need for a metaphysical ground of change, causation, and contingent existence, not merely a first event in time.
• Aquinas’s distinction between essentially ordered and accidentally ordered causal series allows him to avoid some standard objections to cosmological arguments that focus on temporal beginnings.
• The concept of a necessary being or pure actuality offers a unifying explanation for why there is something rather than nothing and why the world exhibits order and stability.

Critics raise several objections:

• Infinite regress: Some deny that an infinite regress of causal or explanatory relations is impossible or incoherent, questioning Aquinas’s rejection of such regresses.
• Causal principles: Empiricist and skeptical philosophers, such as David Hume, challenge the assumption that every change or contingent fact must have a cause or sufficient reason.
• Composition fallacy: Critics suggest the argument may illegitimately move from each member of a set (every contingent thing has a cause) to a claim about the set as a whole (the whole set has a single external cause).
• Conceptual leap to God: Even if a first cause or necessary being exists, opponents contend that further work is needed to show it has the attributes traditionally associated with the God of classical theism (omniscience, omnipotence, goodness, personal agency).
• Modern cosmology: Some argue that contemporary physical cosmology offers alternative accounts of the origin or structure of the universe that do not require a metaphysical first cause, while others maintain that such scientific explanations leave deeper metaphysical questions open.

Because the soundness and even the correct interpretation of Aquinas’s arguments remain disputed, the status of the Thomistic cosmological argument is generally regarded as controversial. It continues to serve as a focal point for discussions about the limits of reason, the nature of causation, and the scope of metaphysical explanation in arguments for the existence of God.