f there is no ultimate cause of a thing or explanation for why something exists -- that is, if the causal sequence is endless or infinite – then nothing would ever happen or be intelligible here and now. But things do happen here and now. So there must be some ultimate cause which itself is not caused by anything else, and that cause is God.Another way to put this: just as each thing or event depends on something else to account for its existence, so also the whole order of things (the universe) must itself depend on something elso to account for its existence. Otherwise, there woud be an infinite regress (and endless chain of causes causing causes) and thus nothing to account for why there is a universe at all. That other thing (God) doesn’t depend on anything for his existence: his existence is called "necessary".Notice: Aquinas’ rejection of an infinite sequence of causes does not apply to the horizontal sequence of causes in history, but rather to the vertical sequence of intelligibility in terms of which some merely possible thing is understandable as actual right now. That is, it is possible that the universe has existed eternally and never had a precise moment when it was created. If that is the case, then the cosmological argument cannot assume an ultimate beginning to history. Rather, in order to account for something’s existence hre and now – either things in the universe or the universe as a totality -–we have to think in terms of a vertical (ontological) terminus or end of causes. Inorder to account for the existence of anything in the universe right now, we have to assume that other things exist right now, and those things can only exist if other things exist right now. This sequence cannot go on indefinitely because there would never be something that ultimately accounts for thing existing right now. But since things do exist right now, there must be such a cause which does not depend on...
