Aristotle, though he did not believe in God as such, developed five inductive, a posteriori arguments which pointed towards a "prime mover". These arguments were later used by St Thomas Aquinas as the basis for his five ways to God, summarised in about a page and a half of his mammoth work the Summa Theologica
(First part, a, Question 2, Article 3). The study of this passage of the Summa
forms the basis of most Philosophy of Religions specifications today in England, Wales, Northern Ireland, Scotland and Ireland and crops up as part of courses in Philosophy, Critical Thinking, Theory of Knowledge and the Study of Religions all over the world. Puts things in context doesn't it; you spend up to two years focussing on something that takes 5 minutes to read carefully, a fraction of one per cent of even one book written by one scholar.
According to Aquinas, the existence of God can be proved in five ways:1. Motion The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.
2. The efficient cause The second way is from the nature of the efficient cause. In the world of sense we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or only one. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God. 3. Possibility and necessity
The third way is taken from possibility and necessity, and runs thus. We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence - which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.
In the first three of the five ways to God Aquinas, drawing on Aristotle, observes order in the universe (the word for order in Greek is Kosmos) and draws a logical conclusion about why that order exists. All cosmological arguments work in this way; they observe order, a principle or law in the universe and then conclude that there must be an explanation for this which is, as Aquinas puts it, what "all men speak of as God". Cosmological arguments may therefore be described as inductive, a posteriori and strong and like all such arguments, the best ways of refuting them is either to demonstrate that the order, law or principle is not present in the universe or to dispute that its cause is what "we call God".