Thomas Aquinas' Five Ways to Prove the Existence of God

General Remarks

• Cosmological Argument: All five ways are considered variants of the cosmological argument, which reflects on the conditions of the universe's origin and structure.
• A Posteriori: The arguments are a posteriori, based on the effects of God's existence known to us, unlike Anselm's a priori argument.
• Teleological Argument: The fifth way is similar to the teleological argument or argument from design.

The First Way: Motion

1. All bodies are either in potential motion or actual motion.
2. Transition from potentiality to actuality requires something already in actuality.
3. Nothing can be both in actuality and potentiality simultaneously regarding motion.
4. Therefore, nothing can move itself, requiring an external mover.
5. Without a first mover, there would be no motion.
6. Since motion exists, a first mover, identified as God, must exist.

The Second Way: Efficient Cause

1. Nothing is the efficient cause of itself.
2. If A causes B, the absence of A means the absence of B.
3. Efficient causes follow an order from the first cause to the ultimate effect.
4. Without a first cause, there can be no ultimate effect.
5. Effects exist, hence there must be a first cause, which is God.

The Third Way: Possibility and Necessity

1. Nature contains contingent beings, which are possible to exist or not.
2. Everything is either necessary or contingent.
3. If all were contingent, at one time, nothing existed.
4. Non-existent beings come to exist only through existing beings.
5. This leads to a contradiction since things exist now.
6. Therefore, not everything is contingent, and a necessary being, God, exists.

The Fourth Way: Gradation

1. Gradation exists among entities; some are better than others.
2. Entities are measured by their closeness to the ultimate form of X.
3. The existence of good implies the existence of a most good.
4. Therefore, there must be a cause for being, goodness, and perfection, called God.

The Fifth Way: Design

1. Natural bodies act towards ends.
2. Entities acting towards ends either have knowledge or are directed by a knowledgeable being.
3. Many natural beings lack knowledge.
4. Thus, an intelligent being must direct all natural things to their ends, identified as God.