Aquinas Is Often Thought Of As Someone With a Precise Or Definite Concept Of God, Someone Who Thinks He Can Explain Just What God Is. and It Is Not Surprising That This Is How He Has Struck People. an Early Biographical Source States That Even As a Child He Was Fascinated By the Question 'What Is God?' 1 and the Question Was One To Which He Came To Offer a Series Of Systematic Answers. His Writings Are Crammed With Assertions About God and His Nature.
Yet a presiding thesis of Aquinas is that, though we can know that God exists (an est), we cannot know what God is (quid est). One might expect that, once he has argued for the existence of God, Aquinas would next proceed to offer a systematic and positive account of God's nature, properties, or attributes. But that is not what he does. In a passage immediately following the text of the Five Ways, he writes:
Having recognized that a certain thing exists, we have still to investigate the way in which it exists, that we may come to understand what it is that exists. Now we cannot know what God is, but only what he is not; we must therefore consider the ways in which God does not exist, rather than the ways in which he does.
The same move is made in the Summa contra Gentiles. Book 1, chapter 13 of the treatise is called 'Arguments in Proof of the Existence of God'. Chapter 14 begins with the assertion: 'The divine substance surpasses every form that our intellect reaches. Thus we are unable to apprehend it by knowing what it is.'
What does Aquinas mean by saying this? To start with, it is important to note that he does not mean what the casual reader is likely to