Does God Exist? This would seem like a simple question. However philosophers, theologians, and ordinary people have struggled since the beginning of time answering it. Cultures, countries, and obviously religions have all stemmed from this "simple" question. There is no "yes or no" answer, at least one that has tangible proof behind it. There have been many philosophers who have spent almost their whole lives developing a proof to solve this riddle. St. Thomas Aquinas is just one in particular who spent much deliberation on proving God's existence. He wrote much of this in his book entitled "Summa Theologica." In fact, he actually came up with five proofs. They proved God's existence through motion, causality, contingency, and from perfection and order. Aquinas" best argument is his second proof saying that God exist through the theory of causality. .
Aquinas" second way of proving the existence of God through causality results in a proof which has five steps to it. First, Aquinas says some events cause other events. The world is a sequence of events. Next, he says that if an event happens, then it must be caused by something outside of itself. Every event that exists has a cause. Event "B" is an effect from the cause of event "A," which was prior to event "B." Event "B" being an effect from the cause of itself is contradictory. Aquinas moves on to state that there can be no infinite cause/effect chain. There cannot be an infinite regress of efficient causes. Then, he pulls these together to say that there is a first, uncaused cause. Finally, he brings his proof to a close by claiming God must exist. .
To explain Aquinas" proof in more detail one must look directly into the converted English text of "Summa Theologica." His first and second premises are explained when Aquinas says, "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.