Vincible and Invincible ignorance
Vincible ignorance is, in Catholic moral theology, ignorance that a person could remove by applying reasonable diligence in the given set of circumstances. It contrasts with invincible ignorance, which a person is either entirely incapable of removing, or could only do so by supererogatory efforts (i.e., efforts above and beyond normal duty).
It is culpable to remain willfully ignorant of matters that one is obligated to know. While invincible ignorance eliminates culpability, vincible ignorance at most mitigates it, and may even aggravate guilt. The guilt of an action performed in vincible ignorance ought to be measured by the degree of diligence or negligence shown in performing the act. An individual is morally responsible for their ignorance and for the acts resulting from it. If some insufficient diligence was shown in dispelling ignorance, it is termed merely vincible; it may diminish culpability to the point of rendering a sin venial. When little or no effort is made to remove ignorance, the ignorance is termed crass or supine; it removes little or no guilt. Deliberately fostered ignorance is affected or studied; it can increase guilt.
Invincible ignorance is used, in Catholic moral theology, to refer to the state of persons who are, through no fault of their own, ignorant of the fact that the Christian message is true.