What is presumption?

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.