Thomas Aquinas

“ The presumption whereby a man presumes inordinately on God, includes self-love, whereby he loves his own good inordinately. For when we desire a thing very much, we think we can easily procure it through others, even though we cannot. ”

“ Presumption does not denote excessive hope, as though man hoped too much in God; but through man hoping to obtain from God something unbecoming to Him; which is the same as to hope too little in Him, since it implies a depreciation of His power ”

“ Contraries are things that are most distant from one another within the same genus. Now presumption and hope denote a movement of the same genus, which can be either ordinate or inordinate. Hence presumption is more directly opposed to hope than to fear, since it is opposed to hope in respect of its specific difference, as an inordinate thing to an ordinate one, whereas it is opposed to fear, in respect of its generic difference, which is the movement of hope. ”

“ Moreover it is conformed to a false intellect, just as despair is: for just as it is false that God does not pardon the repentant, or that He does not turn sinners to repentance, so is it false that He grants forgiveness to those who persevere in their sins, and that He gives glory to those who cease from good works: and it is to this estimate that the movement of presumption is conformed. ”

“ 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. ”