Full Idea
Because we do not know the essence of God, the proposition 'God exists' is not self-evident to us, but needs to be demonstrated by things that are more known to us.
Gist of Idea
We can't know God's essence, so his existence can't be self-evident for us
Source
Thomas Aquinas (Summa Theologicae [1265], Art 1, Obj 3)
Book Reference
'The Existence of God', ed/tr. Hick,John [Macmillan 1964], p.32
A Reaction
Depends on his definition of self-evidence (Idea 21250), which needs knowledge of the essence of the subject. Anselm required 'understanding' of the concept. One might understand the existence criteria without knowing the whole essence. Anselm wins.
Related Idea
Idea 21250 A proposition is self-evident if the predicate is included in the essence of the subject [Aquinas]