I’m often underwhelmed by arguments for the existence of God, often because they are based on natural theology and therefore don’t really give proof of God as Trinity but just a generic theistic god. However, Charles Taylor makes an interesting observation about the distinction between Augustine (with Anselm and Descartes) and Thomas in their arguments that I found interesting:

[Thomas’ proofs] argue to God from the existence of created reality (or what the proofs show to be created reality). They pass, as it were, through the realm of objects. The Augustinian proof moves through the subject and through the undeniable foundations of his presence to himself. (Sources of Self, 141)

The subjective argument of Augustine is this:

my experience of my own thinking puts me in contact with perfection, which at one and the same time shows itself to be an essential condition of thinking and also to be far beyond my own finite scope and powers to attain. There must then be a higher being on which all this depends, i.e., God.  (Sources of Self, 140)

Of course, this distinction makes sense given the respective Platonic and Aristotelian emphases, but I hadn’t considered this difference.