I find Aquinas's argument totally unconvincing. There are two parts to this argument that are left out of the popular version. First, Aquinas argues that nothing can be its own cause. In order for something to be a cause of anything, it must already exist. So, if something were to be its own cause, it would have to exist before it exists " a obvious contradiction. His conclusion then, is not that God is self-caused, but rather that God is uncaused. Aquinas claims in the second part of his argument he attempts to show that the whole chain of the causes must have had a beginning. He points out that if any one of the causes where missing, then everything thing coming after that must never of existed. He follows to say if the first cause was missing then the second, third etc. coming up to the most recent never would have happened. He says that it cannot be infinite. This is true because there could not be a first cause, or second or third or even the most recent one. This is proven that, that theory of it being infinite is ridiculous because if it is infinite and there was no first cause, the most recent one at the moment for me is typing this up, would never of happened. This means that could not be infinite, there must have been a beginning. All Aquinas's has to back up his theory is the fact that he believes in god. It's that belief that makes him believe that there is a first cause. To anyone who does not believe in god, it can just prove to him or her that it makes their view of god not existing stronger.