We will start with the first way put forward by Aquinas for the existence of god. This is known as the way of motion to prime mover. He argued it is certain, and evident to our sense, that in the world some things are in motion. Now whatever is moved is moved by another, for nothing can be moved except it is in potentiality to that towards which it is moved. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be moved from a state of potentiality to actuality, except by something in a state of actuality it is therefore impossible that in the same respect and in the same way a thing should be both mover and moved. This assumes that the potential for something to become something else has to come from outside of itself. For example, a pot will not appear from ball of clay, without the input of a potter! The potential for the pot to be formed from the clay is there, but it requires something external to the clay to work on it to achieve this. Therefore, whatever is moved must be moved by another and cannot move itself. Although a mover must have been moved by another it cannot go on for infinity as there would be no first mover. Aquinas believed there must be a first mover who moves the next mover. For example staff moves only because it is moved by the hand. Aquinas believed this first mover is god. The first way in summary really presumes that something must be moved by another except from the first mover who started it all off which we believed was to be god.
Next Aquinas came up with his second way, arguing from efficient cause to a first uncaused cause. The second way uses the notions of causation and existence. It is much like the first way but instead of motion its replaces it with cause. Aquinas therefore argued that our world in which we live today must have an order of efficient causes. Efficient causes cannot go to infinity due to the causes following in order. The first cause which Aquinas argued was god, so infinity is impossible. He also argued that to take away the cause is to take away the effect. This means if there is no first cause among efficient causes then there are no intermediate causes, suggesting that there would be nothing here, if there was not an original cause of everything. As such, this means that the world and the universe cannot be infinite. The notion of cause and effect means you cannot have the latter without the former. For Aquinas there cannot be an endless regression of cause and effect, and as such there must be a first cause, which is God.
Finally the third way can be explained by contingent being too necessary being. Aquinas’ argument is that if everything were contingent or possible there must have been a time when nothing existed at all. If this was the case nothing could ever could have come into existence since nothing can come from nothing. The fact that there is something as opposed to nothing means that there must be something, in that it existence is necessary and god is this necessary being who created the world out of nothing. For Aquinas, the only thing which has always existed is God. Furthermore, Aquinas saw no way to explain how anything was here, unless something was already in existence prior to it. Thus if God did not exist, nothing else would exist. This means god is the cause of everything which has come into place in our universe and that something had to be here to start the creation of our universe. Without a cause then we wouldn’t be here today. Aquinas argues god Is our only necessary being even though there are criticisms to this.
