Summa Theologiae Moralis, vol. I: De Principiis

S. Th. I-II, q. 6, a. 8; q. 19, a. 6; q. 76.

80. Ignorance properly is a lack of knowledge in a subject capable of it, e.g., astronomy in a priest. It differs 1° from nescience, which is a simple negation of knowledge in an incapable subject, e.g., in a child or a madman;

antecedent concupiscence simply diminishes the voluntary, and not only under the aspect of freedom. Yet they do not speak correctly in this way. Hence Schmitt, in the more recent editions of Noldin’s work, I, n. 53, corrected this somewhat, writing: antecedent concupiscence diminishes freedom. And Salsmans, in the most recent edition of Génicot’s work, changed one word, and in place of concupiscence put passion; but for that reason the doctrine is neither more adequate nor less ambiguous.

2° from error, which is not a mere lack but a positive act of the intellect judging a thing to be otherwise than it is: it arises from ignorance or rashness; 3° from inadvertence, which is a lack not indeed of habitual knowledge but of actual consideration; 4° from forgetfulness, which is the privation of knowledge previously had. Since moralists deal only with duties owed and with sins not owed, they often more strictly take ignorance, not indeed as negation, but as privation of knowledge which ought to be in someone, such as theology for a confessor. Hence some distinguish ignorance negative, and privative, nay even positive or of false disposition, if it includes error.

81. Ignorance is divided: 1) By reason of the object that is ignored, there is ignorance of law, whether natural or positive, whether divine or human, whether of the law itself or of the penalty attached to it: by which, namely, the existence or extension or meaning of the law itself is ignored;— and ignorance of fact: by which a fact or a concrete circumstance of the fact determining the present application of the law is ignored.

Thus, one who does not know that fasting is to be observed on the vigil of Pentecost, or that heretical books are forbidden, is in ignorance of the law; one who does not notice that this day is the vigil of Pentecost, or that this book is heretical, is in ignorance of fact.

2. By reason of the subject, or the person who is ignorant, ignorance is invincible or vincible. Invincible, or involuntary, is that which could not be removed by moral diligence; — vincible, truly, or voluntary, is that which could be so removed.

Moral diligence, however, is that which prudent persons are accustomed to employ, and which varies according to the various circumstances or the quality of the business, person, place, etc., e.g., it will be greater in a priest for duly carrying out his office than in a rustic, greater where the goods of life are at stake than those of fortune, where there is notable harm to a third party than where there is small harm.

Vincible ignorance is blameless if it ought not to be removed;— blameworthy indeed if it ought to be. Moralists, however, attending only to what is owed and not owed, promiscuously use the terms blameworthy and vincible, and often call vincible ignorance that which is blameworthy, and call invincible that which is blameless¹.

Invincibilis can arise from two sources: either because one has not thought at all about the truth to be sought or about the danger of erring (for the first idea is not within a person’s power), or because, if one has thought and applied diligence, one still has not arrived at the truth. Hence it is not voluntary.

On the other hand, vincible ignorance is voluntary either directly and in itself, as when someone wishes to be ignorant; or only indirectly, from negligence, as when one omits to inquire while one ought to inquire; or only in its cause, if one wills something to which ignorance follows (e.g., drunkenness). There are, moreover, many degrees of it, which are commonly reduced to three: a) ignorance strictly or simply vincible when diligence is employed to overcome it but not sufficient or not all that is morally possible, or not all that the quality of the affair and of the person demands: it is indirectly voluntary; b) crass when no or scarcely any diligence was employed to acquire knowledge, and supine if it was so [employed] to drive away ignorance: it is voluntary, either indirectly, or in its cause; c) affected, malicious, or directly willed, when someone expressly and deliberately wishes to be ignorant for whatever end: whether to act at will and not be drawn back from a purpose, or to have an excuse in sins committed or to be committed, or out of weariness, etc., especially if he studiously wishes not to know so that he may not be drawn back from sinning but may sin more freely.

3) By reason of the act of the will, at once in regard to the ignorance and in regard to the deed.², ignorance is:

a) Antecedent [ignorance] which does not follow from the will but precedes its act, and yet is for it the cause of willing and acting what (according to the present disposition) it would not will or do if knowledge were present. Hence ignorance is a cause of the deed because it removes the knowledge which would impede the deed, e.g., if someone, thinking he is killing a wild beast, kills a friend whom he would not have killed had he known: such a one acts from involuntary ignorance. For every antecedent ignorance is invincible, but not conversely, because the invincible is not always a reason for doing what otherwise would not be done.

b) Concomitant [ignorance] which precedes the act of the will and is joined to it, yet not as a cause of willing and doing what is done, because even if it were not present, the deed would nonetheless be done (according to the present disposition), e.g., if someone, thinking he is killing a wild beast, kills an enemy whom he would also have killed had he known: such a person acts with involuntary ignorance. It is also invincible.

c) Consequent is that which in some way follows from an act of the will directly unwilling or indirectly negligent, and it is directly or indirectly voluntary and at the same time precedes the work so that it can be a cause of willing and doing it, e.g., if someone voluntarily neglects to inquire about the danger of killing a man whom, if he knew, he would not kill, or about the day of abstinence when, if he knew abstinence was required, he would abstain: such a one acts from voluntary ignorance. Consequent is vincible, as being voluntary; whether it be vincible at the moment the work is done, or was once vincible, provided the work was foreseen and on account of it the ignorance ought to have been guarded against — otherwise it would be invincible with respect to the work although in itself vincible, and therefore antecedent or concomitant with respect to the work that is done.

82. Principles. 1. Antecedent ignorance removes the voluntary with respect to that which is ignored, because it is invincible; indeed it renders the act positively involuntary simply, because it makes something against the habitual inclination of the will: for the act would not be done if the ignorance were absent. Whence: what is done from antecedent involuntary ignorance is positively and simply involuntary; therefore such ignorance excuses.

We have said: according to that which is unknown, for under another respect it can be voluntary: thus he who kills a man or a friend, thinking it to be a beast or an enemy, voluntarily shoots the arrow, but does not shoot it at the man or the friend, and he who sins with a woman, not knowing that she is joined in marriage, although not of adultery, is nevertheless guilty of fornication.

II. Concomitant ignorance removes the voluntary because it is invincible, but it does not render the act positively involuntary, because it is not against the inclination of the will, and the act would occur even if the ignorance were absent; it therefore makes the act non-voluntary. Hence: what is done with concomitant involuntary ignorance is non-voluntary, and of this ignorance it is said: it does not accuse, nor does it wholly excuse, namely, from the habitual disposition of the will.

III. Consequent ignorance does not make an act simply involuntary, but renders the work simply voluntary, because it itself is vincible and voluntary. It does, however, make in general (even if it be affected) something involuntary in a qualified sense, because it is against some inclination of the will, insofar as it is the cause of doing that which would not be done with knowledge present; hence it diminishes the voluntary and sin according to the degree of vincibility, so that even sometimes it makes a mortal sin venial.

But it should be well noted: ignorance that is exceptional in being voluntary in no way diminishes, if indeed it be so affected as that one precisely chooses it in order to sin more freely or so as not to be held back from sin: this, namely, in no way makes something involuntary, nor accordingly diminishes the voluntary and the sin, but rather increases it, not by reason of itself but by reason of the cause, because a greater disposition toward evil is present. For then, from the greater intensity or more intense inclination of the will toward sinning, it comes about that someone wishes to undergo ignorance.

Hence: what is done from voluntary or consequent ignorance is simply voluntary, but ordinarily involuntary in a certain respect, and then less voluntary. That ignorance does not excuse, but accuses.

83. Observations. — 1. The general doctrine on ignorance is briefly expressed in canon 2202, § 1: “A violation of an unknown law is in no way imputed if the ignorance was inculpable; otherwise, culpability is diminished more or less according to the culpability of the ignorance itself.”

2. What we have said about ignorance can be applied to inadvertence and forgetfulness, and to error. Error includes ignorance; full inadvertence and perfect forgetfulness are equated with invincible ignorance; but if they are not perfect but arise from negligence, they are equated with vincible ignorance. Hence canon 2202, § 3: "What is established about ignorance also holds for inadvertence and error."