There is one last point I want to make contra Richard Dawkin's book before I bring the recent round of theistic gunfire to a halt for a while.
Dawkins says that each of Aquinas' arguments makes the unwarranted assumption that God is immune from whatever deficiency the argument takes as it's starting point (whether it be motion, contingency etc).
This obviously involves quite a misunderstanding on Dawkins' part. The point of the argument is that if there were not a being immune to such defects then there would be no adequate explanation for the observed phenomena. This would violate the self evident first principle of sufficient reason. The principle states quite simply that nothing is without sufficient reason, whether it be the actual existence of the thing in question or the fact that it is motion etc. Of course, if a person denies this principle you can make life hell for them by demanding they remain consistent with themselves. As soon as they seek a cause for something (an activity humans perform regularly) remind them that according to them, they need not do so. If my house suddenly collapsed I wouldn't say "oh it just collapsed because it did didn't it?" No, I would suspect (I would know!) there was a reason it collapsed. It is also goodto point out that it is the principle of sufficent reason not just the principle of reason. I could not go saying "my house collapsed because it felt like it." This would be an insufficient reason. The effect cannot exceed the cause (another one of those self evident truths).
The argument points to the fact that a being immune to whatever deficiency it is we are observing must exist hence it is not an assumption (let alone an unwarranted one) but a necessary conclusion.
To bring out the point more clearly let's go back to our book borrowers. I see a book that is being borrowed by someone. I deduce from this that an owner exists or the book could never be borrowed. Now imagine yourself protesting "Summa, you are making the unwarranted assumption that the owner is immune from the need to borrow the book!" Most people would roll their eyes at such an illogical comment. That being the case it is enough to put Dawkins at bay.
There's a second point I also want to follow up to flesh out a previous post. I said that beings which do not contain within themselves the reason for their existence need a cause. You can see from this sentence why Bertrand Russel's objection "if everything must have a cause then God must have a cause" is not a valid counter argument as no one is saying that everything needs a cause.
How do we know if something does not contain within itself the reason for its own existence (ie it's existence is not self explanatory, thus requiring us to look elsewhere for a cause)? Very simply if you can conceive of something as not being, as not existing, then it possesses the above deficiency. To conceive of a self existent being as not existing would be the equivalent of the intellect trying to conceive of a part greater than its whole.