Invincible ignorance is a theological concept found primarily in Catholicism. Invincible ignorance denotes a lack of knowledge for which someone is not held morally responsible. He is blameless because of one of a variety of excuses, which might include scarcity of evidence, or inadequate talent, or the difficulty of the subject matter. This is in contrast to vincible ignorance which can be removed with reasonable effort.  It is not to be confused with the fallacy of invincible ignorance.