Objection 1: It would seem that presumption does not arise from vainglory. For presumption seems to rely most of all on the Divine mercy. Now mercy (misericordia) regards unhappiness (miseriam) which is contrary to glory. Therefore presumption does not arise from vainglory.
Obj. 2: Further, presumption is opposed to despair. Now despair arises from sorrow, as stated above (Q. 20, A. 4, ad 2). Since therefore opposites have opposite causes, presumption would seem to arise from pleasure, and consequently from sins of the flesh, which give the most absorbing pleasure.
Obj. 3: Further, the vice of presumption consists in tending to some impossible good, as though it were possible. Now it is owing to ignorance that one deems an impossible thing to be possible. Therefore presumption arises from ignorance rather than from vainglory.
On the contrary, Gregory says (Moral. xxxi, 45) that "presumption of novelties is a daughter of vainglory."
I answer that, As stated above (A. 1), presumption is twofold; one whereby a man relies on his own power, when he attempts something beyond his power, as though it were possible to him. Such like presumption clearly arises from vainglory; for it is owing to a great desire for glory, that a man attempts things beyond his power, and especially novelties which call for greater admiration. Hence Gregory states explicitly that presumption of novelties is a daughter of vainglory.
The other presumption is an inordinate trust in the Divine mercy or power, consisting in the hope of obtaining glory without merits, or pardon without repentance. Such like presumption seems to arise directly from pride, as though man thought so much of himself as to esteem that God would not punish him or exclude him from glory, however much he might be a sinner.
This suffices for the Replies to the Objections.