B. Perjury is a Mortal Sin

1. Solution

12. Hence follows the proposed conclusion about perjury, because to bring in God as witness of what is false is to do irreverence to God: - either by bringing him in as a witness ignorant of the truth and so not omniscient, or bringing him in as willing to testify to what is false and so not completely truthful. In either way irreverence is done immediately to God, against the commandment of the first table, “Thou shalt not take the name of the Lord thy God in vain” [Exodus 20.7]. And so, in either way, if done deliberately, it is a mortal sin.

2. Two Doubts Against the Aforesaid

13. But here there are two doubts. The first is whether perjury’s not being deliberate excuses it from being a mortal sin. Second whether one sins mortally by bringing in God as witness in the aforesaid way for anything that one believes to be true though it is not true, or for something about which one has some opinion but assents rather to the opposite.

a. About the First Doubt

14. As to the first of these doubts it is commonly conceded that a single slight perjury is not a mortal sin.

15. However, to be a perjurer habitually is a mortal sin. And this it seems can be proved, because a habit generated by many acts inclines one to a graver act than are the preceding ones.

16. But against this: if the first act of perjury is not a mortal sin, then neither is any other, even from whatever habit it comes to be, because an inclining habit cannot make an act graver. For if someone acquired a great habit from acts of incontinence and quickly repent, then if after repentance he have some movement of incontinence, although his great habit incline him to it, yet it is not a mortal sin in him; indeed neither is it notably graver than it would be in someone else who has no habit.

17. A confirmation is that a habit cannot be graver, if it has any gravity. Since however gravity has no culpability, properly speaking, save from acts, then since the acts from which the habit is generated are venial, the habit will not produce any mortal gravity in acts elicited by the habit.

18. It seems then possible to say that a habit or custom does nothing for the proposed conclusion. But perjury, with full consent, is against the commandment of the first table and consequently turns one aside immediately from the ultimate end, and so nothing of the idea of mortal sin is lacking to it.

19. But if a perjury is not done deliberately, however often it is done, then since a meritorious act requires that it be fully human and so fully deliberate, an act of demerit would require altogether the same (for God is not more prone to punish than to condone) - if so, one can say that a non-deliberate perjury, even repeated ever so often, is not a mortal sin.

20. However, as was said before in the material about the virtues [d.33 n.77], a virtuous man has quick deliberation (which does not seem to be deliberation because of its quickness), because he has great prudence wherewith he is prompt to deliberating as it were in imperceptible time. So too someone could, from a habit opposite to prudence, acquire for himself a facility in deliberating promptly about the opposite, as if in imperceptible time, and this deliberation, following the habit, would be sufficient for the idea of sin; just as the like deliberation in a good man would be sufficient for the idea of merit.

21. Therefore, as concerns the idea of mortal sin, I do not distinguish so much between the rarity or frequency of perjury as between its deliberation or lack of deliberation, so that when deliberation is concurrent it makes mortal sin (and that whether the act is single or customary), and lack of deliberation excuses, whether once or as many times as you like.

b. About the Second Doubt

22. As to the second doubt [n.13] I say that he to whom one swears either accepts (from positive law or common custom) that the oath is as it were simply assertive of what is sworn, or that it is not as it were simply assertive but induces to probable belief of the thing sworn.

23. In the first way I say that one who swears something that is in any way doubtful (that is, something not simply certain and true and deliberate) sins mortally, because he is bringing in God as witness to confirm that what he asserts is simply certain and true when it is not simply certain.

24. And in this way must be understood all oaths of those who swear in court, where the sort of sentence accustomed to be passed there should not be passed unless what is asserted is simply certain. For example, a sentence of death should not be passed save for a crime that is certain. Therefore, he who swears that the accused is guilty of the crime when he is not certain, however much he may nevertheless conjecture that the accused is guilty and swears this in such a forum (where, by positive law or custom, a condemnation to death follows), he sins mortally. The like holds of any forum where (from the fact someone is convicted through sworn oaths) the accused is condemned as simply guilty or as infamous with the infamy of law. For in this case not only is irreverence done to the name of God against the commandment of the first table, but there is a pernicious lie because harmful to one’s neighbor [cf. d.38 n.23].

25. And if you say ‘it is useful for the republic; otherwise evil people will be too much multiplied’, God replies “You will execute what is just justly” [Deuteronomy 16.20]. For there are certain evils that are not to be punished by men but are to be left to divine vengeance - for instance all things where man, as man, cannot even sufficiently teach the truth in the way it ought to be taught for the purpose of justly passing a due sentence of punishment. Nor are the witnesses alone guilty in these cases but the judge too. And if a judge knows that by custom witnesses only swear under oath what they believe, then he should not pass such sentence as should be passed if guilt were simply proved before him. For he knows from custom that guilt is not proved before him sufficiently for the infliction of such a punishment.

26. But if by positive law or custom it is held that a sworn witness is not bound to depose what he is certain of but only what he believes, then the swearer does not sin, provided he make conjecture for this side rather than another from probable signs. The point is contained in Gregory IX Decretals I tit. 12, about making examination for holdy orders, where Pope Innocent replies, “as far as human fragility allows us to know, [the Church] both knows and testifies that this man is worthy of the burden of this sort of office.” Hence Pope Innocent says that

“in making such response we do not believe that anyone sins, provided he not speak against his conscience; for he does not assert simply that the candidate is worthy but asserts it as far as human fragility allows one to know, since one should judge him worthy whom one does not know to be unworthy.”

27. Therefore, in such promotions either to any dignity of office by election or to holy orders, or also in other colleges (as to mastership in universities, to prelacy in religions, or to other acts of the sort), if there is an approved custom that the responses of the respondents (under proffered oath, or under pledge of faith, or under promised obedience) should be understood only of belief ‘as far as human fragility permits us to know’, and that the presider does not know of any indignity in the candidate, then all such responses should be understood according to the common custom and the respondents do not sin in anything (though it would be safer to speak there with some qualification, as in the aforesaid Decretal, that one speaks not simply but as far as human fragility allows). And in such cases a judge who promotes such a candidate does not sin, because the custom is that giving such testimony of one’s belief is enough.

28. Here then ‘favor is enlarged and hatred is restricted’ according to the maxim of the law [Boniface VIII Decretals 6.V tit.12], because in matters of hate a sworn witness should speak the truth strictly, and a truth that is certain, for otherwise it is not a reason that the sentence of condemnation afterwards passed should be passed. In favorable matters it is sufficient for the person sworn to say what he believes to be true, above all where the custom or positive law in the college is of the sort that one speak one’s belief. For because of the truth as to belief thus testified, the presider can promote the candidate to such and such a rank.

29. Now universally, whether in favorable or hateful things, he who swears something the opposite of which he more believes than anything else, swearing even to that about which he is simply doubtful and where he does not assent in his heart more to one side than the other - such a person sins mortally in swearing, because he brings in God as witness for something he is in no way certain about which he ought to be certain about.

3. Third Doubt against the Aforesaid

30. If objection is raised against the statement that perjury is against a commandment of the first table, for it seems that according to Master Lombard [III d.39 ch.3 nn.1-2] perjury is a sort of lie and so against the commandment of the second table, “Thou shalt not speak false witness against your neighbor” [Exodus 20.16] - one can reply that in perjury there is a double sin: namely a lie or lying as material, and the taking of the Lord’s name in vain, that is, taking it not only uselessly but irreverently and against reverence. The first sin belongs to the second table but the second belongs formally to the first table, because of the irreverence prohibited there.

31. Perjury is also possible without lying, for example, where he who simply doubts swears to the part he doubts - which would not be a lie if he asserted it, for he does not have the opposite in his mind. At any rate, in a case where the swearer is bound to be certain, he commits perjury if he is not certain, and yet if he asserted it without an oath he would not lie because he does believe it more than the opposite.

32. It is dangerous therefore to have an oath frequently on one’s lips, because, in the case of many statements, there would be no sin without an oath, but there is sin when an oath is added, and grave sin if done deliberately [n.21]. Therefore useful is the counsel of our Savior, Matthew 5.37, “Let your speech be yea yea, nay nay.”