Article I: On Ignorance

373. Does ignorance excuse from fault? - Ignorance on the part of the subject does not effect that the law does not touch him in first act, but it can effect that it does not obligate in second act and that the transgressor is excused from fault. For invincible ignorance (antecedent or concomitant), whether of right or law, or of a fact determining the application of law, excuses from fault because it takes away the voluntary: for nothing is willed unless foreknown. On the contrary, vincible ignorance does not take away the voluntary; nevertheless it diminishes fault, unless it is affected for sinning more freely or for having an excuse from sin (n. 82).

374. Does ignorance of law excuse from penalty? - Invincible ignorance, whether of right or of fact, in the internal forum excuses from penalty because it excuses from fault; on the contrary, vincible ignorance does not excuse from a proportionate penalty, yet it excuses from a disproportionate penalty; whence if the fault is light, a grave penalty is not incurred (can. 2199-2203). But in the external forum, "ignorance or error concerning the law or penalty or concerning one's own fact or concerning another's notorious fact is generally not presumed; concerning another's non-notorious fact it is presumed until the contrary is proved" (can. 16, § 2); and "once an external violation of the law is posited, malice (that is, a deliberate will of violating the law) is presumed in the external forum until the contrary is proved" (can. 2200, § 2). This often does not happen, and therefore (if sufficient proof is lacking) someone is sometimes bound to undergo a penalty on account of a just cause, the common good demanding it, at least when the sentence of a judge is added; but then it is not a penalty properly so called, but rather a burden to be undergone on account of the common good.

1. Indeed, according to present-day right, none is incurred if there is question of laws properly so called (not of mere precepts) and of penalties of latae or ferendae sententiae to be inflicted by a judge (not by a superior), even in the external forum, if the excuse is established for the external forum (can. 2218, § 2).

375. Does ignorance of the penalty excuse from the penalty? - Ignorance (even invincible) of the penalty alone does not excuse from a proportionate penalty, because reason dictates to each person that evil according to its nature is to be punished, e.g., homicide by death, theft by prison. Whence canon 2202, § 2: "Ignorance of the penalty alone does not take away the imputability of the delict, but diminishes it somewhat." Similarly it does not excuse from invalidation, for canon 16, § 1: "No ignorance of invalidating or inhabilitating laws excuses from them, unless something else is expressly said." Indeed, neither does ignorance of the law exempt from any vindicative penalty of latae sententiae in the external forum (can. 2229, § 3, 1); whence canon 988: "Ignorance of irregularities, whether from delict or from defect, and of impediments, does not excuse from them."

Nevertheless, ignorance of law or penalty excuses: a) if the penalty supposes contumacy and therefore knowledge of the threat, as for medicinal penalties and censures, unless the ignorance is crass or supine (can. 2229, § 3, 1); b) if the legislator requires knowledge or rashness, because he does not will to punish except him who has acted knowingly, rashly, deliberately, studiously, with presumption, or has dared (can. 2229, § 2), unless the ignorance is affected, because this in law is equated with knowledge and excuses from no penalty of latae sententiae (can. 2229, § 1).