St. Thomas Aquinas is most famous for his Five Ways. He regarded that the ontological argument as invalid. We cannot prove that God exists, merely by considering the word God, as the ontological argument in effect supposes. For that strategy work, we would have to presume to know God’s essence. The proposition of God exists is not self-evident to us mere mortals. Although people can prove God’s existence in several ways, we cannot do it just by examining the concept of God. We have to consider what it is about nature that makes it manifest that it requires God as its original cause. According to Aquinas, the existence of God can be proved are in fact five, and it is his most famous “Five Ways”
The first way to prove that God exists is to consider the fact that natural things are in motion. According to Aquinas, a first mover must exist. If first mover do not exists, there would be no other mover and nothing would be in motion. It means all the natural things are in motion, and it needs another moving thing to move it. As we look around the world and survey move things, it becomes clear that they do not put themselves into motion. But all things are all in motion, and they cannot move by their own, therefore, a first mover must exist and it is not moved by other, and that thing is God.
The most important idea Aquinas wants to say is that things do not put themselves into motion, do not suppose that he thought that people cannot get up out of their chair and walk across the room. He means that things do not just bring themselves into existence, there must be someone put themselves into motion.
The second way of proving God’s existence is kind of similar to the first one. Aquinas says in the world of sensible things, nothing causes itself. It means everything is causes by something else. It has to be a first cause, if there have no first cause exist, there would be no first effect. In fact, there would be no second or third effect either. If first causes must exist, then we must admit that is God.
Aquinas did not say anything in either of the first two proofs about things being moved or caused by earlier motion or causes. The various motions and causes he is talking about are simultaneous. In Aquinas’s opinion, there is no philosophical reason that the chain of causes could not go back infinitely. But there cannot be an infinite series of simultaneous causes or movers. His argument is that things must be causes by something earlier, and because this chain of causes cannot go back infinitely, therefore, it must have a first cause, and it is God.
The Big Bang theory is a good example to proof Aquinas’s theory. The Big Bang is accepted by most scientists that the universe is an explosion. The Big Bang is the beginning of space and time of matter and energy, and it is the beginning of our expanding universe. But the universe does have an absolute beginning, which was a first physical event. It is difficult to believe that the first physical event has no explanation, for that amounts to saying that the entire universe is just a chance occurrence. If the physical event is explicable, then it would seem that the explanation must refer to some sort of nonphysical phenomenon, which is “God”.
The third way is the most complicated of the Five Ways, God is the necessary of our being existence. Aquinas says everything can lay our hands on belongs to “need-not-exist” category, if everything belongs to this category, then at one time nothing existed, and then it would have been impossible for anything to have begun to exist, and thus even now nothing would exist. There must exist something the existence of which is necessary. Aquinas believed that he had not yet ruled out the possibility that the necessity of this necessary being might be caused by another necessary being, whose necessity might be caused by another. He asserted that it is impossible to go on to infinity in necessary things which have their necessity caused by another. Therefore, he concludes that there must be some necessary being that has its own necessity, and that is God.
Aquinas’s first three proofs of God’s existence are versions of what today is called the cosmological argument. The cosmological argument is actually not one argument but a type of argument. This type of argument means that the existence of contingent things, things that could possibly not have existed, points to the existence of a noncontingent or necessary being, God, as their ultimate cause or source of being.
Aquinas’s fourth way to prove God is the gradation to be found in things. It has to consider the fact that all natural things possess degrees of goodness, truth, nobility, and all other perfections. The gradation in things in the sense that something can be more good. Therefore, there must be that which is the source of these perfections, namely, pure goodness and truth, and this is what we call God.
The fourth proof about the existence of goodness or good things is called the moral argument. This argument is supporting the existence of God, it argues that God is the best and is the only explanation for morality. God is the best moral for everything; God must exist to support that moral order exists.
The last way to proof of God’s existence is predicated on the observation that natural things act for an end or purpose. That is, they function in accordance with a plan or design. Accordingly, an intelligent being exists by which things are directed toward their end, and this intelligent being is God.
Arguments like Aquinas’s fifth proof, according to which the apparent purposefulness or orderliness of the universe or its parts or structure points to the existence of a divine designer, are called teleological arguments. The teleological argument suggests that, given this premise, the existence of a designer can be assumed, typically presented as God.
According to Aquinas, some theological truths, truths of revelation, are such that philosophy could never discover them. For example, philosophy cannot establish that the universe had a beginning and is not eternal. And not everything discovered by philosophy is important for salvation. But philosophy and theology, although separate