The Five Ways
Thomas Aquinas, Summa Theologica I, q.2, a.3 · c. 1265
Aquinas's five arguments for the existence of God, from motion, causation, contingency, gradation, and final ends.
The existence of God can be proved in five ways. The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another.#
If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.#
The second way#
The second way is from the nature of the efficient cause. There is no case known in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.#
The fifth way#
The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.#