Aquinas' Five Ways: Proving the Existence of God

The Second Way: The Argument from Efficient Causes

In the world of sense, there is an order of efficient causes.

• No thing can be an efficient cause of itself, as it would be prior to itself, which is impossible.
• One cannot proceed indefinitely in the series of efficient causes. If you remove the cause, the effect disappears. In the order of efficient causes, the absence of the first cause would mean the absence of the middle and the last causes.
• If we were to carry the series of causes to infinity, there would be no first efficient cause, no ultimate effect, and no intermediate causes.
• Therefore, it is necessary to admit a first efficient cause: Et hoc dicimus Deum (and this being is God).

The Third Way: The Argument from Contingency

Experience shows that things can exist or not exist; they are contingent and can be produced or destroyed.

• It is impossible for things subject to the possibility of non-existence to always exist.
• Therefore, there was a time when nothing existed.
• If things exist now, there must be a necessary being. This being cannot derive its necessity from another, as that would lead to an infinite regress.
• There must be an absolutely necessary being whose cause of existence lies not in another but in itself, and which causes the existence of others: Et hoc dicimus Deum (and this being is God).

The Fourth Way: The Argument from Degrees of Perfection

Goodness, truth, nobility, and other values are found in things in varying degrees.

• The "more" and "less" are predicated of things based on how closely they approximate a maximum (just as "hot" is said of what is closer to maximum heat).
• The perfection we find in beings cannot have its origin in something less perfect; the perfect cannot come from the less perfect.
• Therefore, there is something in all beings that is the cause of their existence, their goodness, and every other perfection: Et hoc dicimus Deum (and this being is God).

The Fifth Way: The Argument from the Order of the World

We see that there are things that have no knowledge, such as natural bodies, which act toward an end.

• This is verified by observing how they often act in the same way to achieve the best result; reaching their goal is not random, but intentional.
• Things that lack knowledge cannot move toward an end without being directed by someone with knowledge and intelligence (as the arrow is directed by the archer).
• There is, therefore, an intelligent being by which all things are directed to order: Et hoc dicimus Deum (And this being is God).