Originally posted by Wajoma
Didn't he try to redefine god as truth, truth exists - therefore god exists?
Not a theory I ascribe to.
The concept of god is the concept of god - the truth is the truth.
I am not an expert, but I don't think that is quite correct. From your post, I would assume you've heard his argument for the existence of God from degrees of perfection: "among beings there are some more and some less good, true, noble and the like. But 'more' and 'less' are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest."(SummaTheologica I.2.3) In other words, since we call things more or less true/good there must be something perfectly true/good we are measuring them by.
However, St. Thomas did not define God exclusively as truth. He actually defines God most precisely as being, or act. This is a brilliant insight, for it ties the Biblical understanding of God to the logical or philosophical understanding of God. In the Old Testament, God reveals His name to Moses: "I am who am." At first glance, this seems very odd - God names Himself with the verb "to be." However, it makes more sense when one considers Aristotle's famous first mover argument. That is a whole separate discussion, though it is connected to his understanding of God as truth.
Before considering that, it may be helpful to look at one of the many ways St. Thomas defines truth: a "certain equality between the understanding or sign and the thing understood or signified."(ST II-II.109.1) In other words, what you think/know is true when what you think/know about a thing corresponds to the way it actually is in reality.
In answer to the question "Whether God is truth?" he cites John14:6 in support of his conclusion and then states that "truth is found in the intellect according as it apprehends a thing as it is; and in things according as they have being conformable to an intellect. This is to the greatest degree found in God. For His being is not only conformed to His intellect, but it is the very act of His intellect; and His act of understanding is the measure and cause of every other being and of every other intellect, and He Himself is His own existence and act of understanding. Whence it follows not only that truth is in Him, but that He is truth itself, and the sovereign and first truth."(ST I.16.5)
A lot to unpack there, as you see. I don't trust myself to give a thorough explanation, but hopefully it gives you a more accurate idea of his position.