Full Idea
A proposition is self-evident because the predicate is included in the essence of the subject. E.g. Man is an animal, because animal is included in the essence of man.
Gist of Idea
A proposition is self-evident if the predicate is included in the essence of the subject
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
Aquinas focuses on the essence of the subject, where Kant embraces the whole concept of the subject. Is it self-evident that we are genetically related to apes? Yes, to a geneticiist. Is that part of human essence? No. So Kant wins.
Related Ideas
Idea 20291 If the predicate is contained in the subject of a judgement, it is analytic; otherwise synthetic [Kant]
Idea 21251 We can't know God's essence, so his existence can't be self-evident for us [Aquinas]