PERJURY. - 1. Notion and morality. - In the specific sense, perjury is only the sinful oath defective in truth as to its object, that is, the oath upon what is false, prescinding from the presence or absence of other moral deficiencies.
In this sense - the only one of interest here - perjury is always a grave sin against the virtue of religion (v.), even if the lie that one wished to confirm by oath is in itself a light sin against the virtue of truthfulness. For the irreverence done to God is always grave when He is invoked as witness to a lie.
The gravity of the irreverence is evident at least in one who truly had the will to call God as witness to his assertion and consciously asserted what is false. There is the case of one who - especially if under another's provocation - recited the oath formula upon what is false, but without having the interior will to invoke God as witness to his lie, in which case pronouncing a feigned oath. Even in this case it is a matter of perjury according to the opinion common among Catholics, for the following reason. The adoration, which from every oath rises up to God, derives not so much from the will of the one swearing as from the fact that those who hear an oath formula pronounced are necessarily led to recognize in it - whatever the interior intention of the one pronouncing it - a public profession of his faith in the absolute truth and truthfulness of God, and such a profession of faith, objectively connected to every oath formula, when this is recited upon what is false, represents a form of simulated idolatry (v.). And this is always a grave sin. So true is this that anyone who came to discover the falsehood would not hesitate to see in that oath formula a grave insult done to God, without asking at all what the will of the one swearing falsely may have been. That formula would sound like an indirect blasphemy (v.), which is always a grave sin. One who, foreseeing the perjury of a person, nevertheless provokes his oath, also sins by perjury, by reason of cooperation in another's sin; unless he is constrained to exact the oath either by obligation of office or for a proportionately grave reason: his cooperation is then only material.
2. Object and effects
The object of perjury is the false; not in the objective meaning of error, but in the subjective meaning of lie. So that it is not perjury to swear to a false assertion, but one believed true; thus, conversely, it is perjury to swear to a true assertion, but believed false and sworn as a lie. When, for the necessity of concealing one's thought from others, the use of mental reservation is lawful, it is likewise lawful to confirm it with an oath. It is clear that, since there is then no lie, there can be no perjury either. The degree of certainty required, for an assertion to be sworn, must be proportionate to the gravity of the motives inducing the oath. But in general, even for an oath, that moral certainty suffices which is enough for the security of ordinary human relations. In a promissory oath the truth consists only in the existing will to fulfill the obligations arising, by justice or by fidelity, from the sworn promise. Their actual fulfillment, according to the common opinion against the view of a few authors, is not part of it. If, however, it does not constitute perjury, there remains the sin against religion because of the violated oath.
By force of the juridical principle iuramentum sequitur naturam actus cui adicitur (can. 1318), from perjury there arise obligations even of religion only, and to the extent to which the obligations of justice or of fidelity arise from the promise. But if the perjury is also a feigned oath, it produces no religious obligation, without however influencing in any way the effects of the promise. In any case, moreover, even when through the defect of some element required ad validitatem, neither the oath nor the promise produces the corresponding obligations, by force of the natural law which forbids harming the interests of others in any way, any damages must be repaired, which, where deceit intervenes, are to be interpreted according to can. 1321.
The canonical penalties against perjury in general are sanctioned in can. 2323; for judicial perjury in can. 1743 § 3. Under Italian criminal law, perjury is an offense relevant only as against the parties in a trial in accordance with art. 371.
Bibliography2 works
Leonardo Azzolini
GOLDEN SPUR (Pontifical Order of the Golden Militia): v. ORDINI EQUESTRI PONTIFICI.