St. Thomas Aquinas, studying the works of the Greek philsopher Aristotle, concluded from common observation that an object that is in motion (e.g. the planets, a rolling stone) is put in motion by some other object or force. From this, Aquinas believes that ultimately there must have been an UNMOVED MOVER (GOD) who first put things in motion. Follow the agrument this way:
1) Nothing can move itself.
2) If every object in motion had a mover, then the first object in motion needed a mover.
3) This first mover is the Unmoved Mover, called God.
Second Way: Causation Of Existence
This Way deals with the issue of existence. Aquinas concluded that common sense observation tells us that no object creates itself. In other words, some previous object had to create it. Aquinas believed that ultimately there must have been an UNCAUSED FIRST CAUSE (GOD) who began the chain of existence for all things. Follow the agrument this way:
1) There exists things that are caused (created) by other things.
2) Nothing can be the cause of itself (nothing can create itself.)
3) There can not be an endless string of objects causing other objects to exist.
4) Therefore, ther must be an uncaused first cause called God.
Third Way: Contingent and Neccessary Objects
This Way defines two types of objects in the universe: contingent beings and necessary beings. A contingent being is an object that can not exist without a necessary being causing its existence. Aquinas believed that the existence of contingent beings would ultimately neccesitate a being which must exist for all of the contingent beings to exist. This being, called a necessary being, is what we call God. Follow the argument this way:
1) Contingent beings are caused.
2) Not every being can be contingent.
3) There must exist a being which is necessary to cause contingent beings.
4) This necessary being is God.
Fourth Way: The Agrument From Degrees And Perfection
St. Thomas