Error is always ignorance. However, while one kind of ignorance is a simple negation of knowledge, error adds to this negation the force of understanding moved by the will. The aim is to fabricate a being in place of absent knowledge, and thus allow ourselves to imagine that we know. But not knowing, and telling ourselves we do know, is a hidden lie of pride. Every formal error, therefore, is a secret act of pride; every error is essentially pride.
Antiquity, in order to differentiate this negation of knowledge from simple ignorance, called it appropriately 'privation'.
[Antonio Rosmini, Certainty, Cleary & Watson, trs., Rosmini House (Durham: 1991), p. 210 (section 1362).]