Question and Answer
May one hide a part of the truth when swearing under oath?
An affirmative oath is the calling on God as witness to the truthfulness of one’s statement concerning a past event. The purpose of an oath is the confirmation of a certain truth, and as such is based upon the divine attribute of omniscience. God, knowing all things, cannot be deceived. An oath confirms the truth of one’s affirmations, for no one can be presumed to be culpable of such impiety and irreverence as to call upon God as witness to a falsehood, and thus to subject himself to the justice of the Almighty.
It is of faith that oaths are licit under the right conditions, in particular when there is a proportionate reason, as is the case when witnesses are asked to swear under oath in a court of law. Moreover, such oaths are virtuous, being acts of the virtue of religion. The taking of God as a witness is, indeed, a profession of His indefectible truthfulness and His universal omniscience. However, the converse is also the case. The taking of an oath to a falsehood is not just a venial sin, as is a lie, but a mortal sin against the virtue of religion. Moreover, there is no light matter in such a sin. Any falsehood stated under oath, even one of lesser importance, is a mortal sin against the virtue of religion.
Theologians state that there are three conditions for an oath to be licit, as explicitly declared by the prophet Jeremias (4:2). These are also explicitly stated in the 1917 (Canon 1316) and 1983 (Canon 1199) Codes of Canon Law. The first condition is the judgment of prudence as to whether there is a sufficient reason to swear an oath, so that it is truly an act of reverence of the divine majesty. Swearing the truth for trivial reasons is a venial sin. Clearly, there is a sufficient reason when a witness swears in a court of law. The common good requires it. The second condition is that it is a just and honest thing to swear, and not something evil (e.g. heresy) or simply the revelation of another’s hidden fault, so as to destroy his reputation.
The third and most important condition, which concerns us here, is that of truthfulness. By truthfulness is meant not only that the sworn assertion is in conformity with the external reality, but also that it is in conformity with the mind of the person who swears to the truth. For truthfulness on the part of a witness excludes all lies, that is, speaking against one’s own mind or personal conviction, but it does not exclude all error. Consequently, a person who swears to an erroneous statement that he is firmly convinced is true does not commit the sin of perjury, whereas a person who swears to a statement that happens to be true although he believes it to be false does commit the sin of perjury. Moreover, a person can only swear to something as certain when he is truly convinced that it is certain, and not just doubtful or probable. If he thinks that it is only probable, or that it is doubtful, then he must state as much, and not mislead others under oath into thinking that it is certain, again under pain of perjury.
The purpose of an oath being to guarantee that the witness’s statements are in conformity with his personal conviction as to the objective truth, it is customary in English to administer it with the expression: “Do you swear to tell the truth, the whole truth and nothing but the truth?” Although not essential to an oath, it emphasizes that the witness in his assertions of answers to questions must tell the entire truth that is on his mind without suppressing a part of the truth (=the whole truth), nor misleading by suggesting something that is not true (=nothing but the truth). In this way, mental reservations are excluded.
There are two kinds of mental reservation. A mental reservation in the strict sense exists when the witness limits the meaning of the words to a special meaning that is not manifested outwardly and cannot be figured out from the circumstances. It is quite simply a lie and is never permissible. Innocent XI condemned the contrary opinion in 1679, namely, the opinion that the person who swears in this way “does not lie and is no perjurer” (Prop. 26, Denzinger 1176).
A mental reservation in the broad sense exists when the limitation of the meaning of the words to one particular sense can be deduced from the circumstances of things, persons, and places, as for example when a physician testifies under oath that he knows nothing, meaning by this that he knows nothing that he is able to reveal, since knowledge in this case is under a professional secret. In such a case, it is not a lie. However, the use of such a mental reservation is not permissible without a proportionately grave reason, and then only provided that there is no intention to deceive and that there is no other honest means of protecting a secret to which one is bound, or some other right due in justice. Furthermore, when an oath is sworn, a major and grave reason is required to use such a mental reservation in the broad sense, on account of the reverence that is due to the holy name of God (Merkelbach, Th. Mor., II, §860).
A witness called to give evidence in a court of law will consequently commit the crime of perjury if he uses a mental reservation that the judge and jurors cannot possibly understand, for example if he were to say that he met the accused on the day in question, understanding in his own mind a meeting by video-conferencing, but allowing everybody else to understand that he met him in person. This is a mental reservation in the strict sense, which nobody could understand. If he were to use a mental reservation in the broad sense without sufficient reason, he would be likewise guilty of a sin against the virtue of religion. This is what Father Merkelbach has to say about this case: “He who uses a mental reservation (in the broad sense) without sufficient reason moreover commits a lie because, if there is not sufficient reason, the circumstances do not sufficiently indicate the restriction in the meaning of the words placed in the mind. Hence he who confirms such a statement with an oath, commits perjury strictly speaking” (ibid., §861).
The attempt to hide a portion of the truth or evidence in a sworn testimony by a witness is effectively a mental reservation, allowing the judge and jury to think that he has given all the relevant information when in fact he has not. If he deliberately omits the cause of an accident or an important circumstance in a crime it would usually be with the intention of deceiving the judge and jury. If this evidence pertains in some way to the substance of the case, such as why an accident happened, or what kind of crime was committed, or how the crime was committed, then it is perjury. It will generally be a mental reservation in the strict sense, which is equivalent to a lie. However, there are occasions in which it is a mental reservation in the broad sense, as for example when a criminal pleads “not guilty” to a crime that he committed. This could be understood, and even expected, by anybody. In the case of the criminal who pleads “not guilty,” there is a proportionately grave reason, and everybody understands that nobody is bound to accuse himself in a court of law.
This will not easily be the case for other kinds of broad mental reservations. Firstly, it is very difficult to be sure that they are broad and not strict. If they truly are broad, it is also necessary that there be no deception involved. However, if some information is hidden, then there is in general the intention to deceive or lead astray, at least to some extent. In such a case, even if it is a broad mental reservation, it is illicit, and is effectively the same thing as a lie. The usual motives for such a mental reservation under oath are the safeguarding of property, or obtaining a larger financial settlement. These are not sufficient to justify a broad mental reservation, as is clear from the following statement, also condemned by Pope Innocent XI: “A just reason for using these ambiguous words exists, as often as it is necessary or useful to guard the well-being of the body, honor, property, or for any other act of virtue, so that the concealing of the truth is then regarded as expedient and zealous” (Prop. 27, Dz. 1177).
In conclusion, therefore, it will not be licit to swear under oath and at the same time to hold back a substantial fact or cause or piece of information or other truth which concerns the case upon which one is a witness, unless it is clear that one has a right to withhold that information, and there is no other way of doing it (such as refusing to testify) and there is a grave reason to do so (e.g. the protection of the professional or confessional secret). A witness under oath must consequently tell everything that is relevant to answering the questions asked or the facts upon which he is making sworn deposition.