The Five Ways
summa theologiae, governance of things, causation, motion, possibility, necessity
Aquinas offered ‘Five Ways’ that are the five proofs or demonstrations near the beginning of his Summa theologiae to establish the existence of God. Some scholars think that Aquinas's Five Ways are meant to demonstrate the existence of the particularly Christian God. Others treat Aquinas's Five Ways as attempts to demonstrate the existence of something omniscient, omnipotent, and wholly good. The First Way focuses on the motion in which he argued that there exist some things that are moved, for anything that is moved, it be moved by something not identical with it, a series of movers does not regress infinitely and therefore there must be a first unmoved mover. Aquinas's Second Way focuses on efficient causation in which he argued that there is an ordered series of efficient causes among sensible things, it is impossible that a thing is the efficient cause of itself, and it is not possible for an ordered series of efficient causes to continue infinitely. Aquinas mentioned that his Third Way is from possibility and necessity, but one must be careful how to understand ‘necessity’ or ‘possibility’, as one shall see. Aquinas's Fourth Way mention that there are things that are more or less good, more or less true, more or less noble, and so on, there is something maximally good, maximally true, and maximally noble, which is maximally true is maximally being and there is something which is maximally being. The Fifth Way, and final way, is from the governance of things.
The Oxford Handbook of Aquinas