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Secular use 
Mental reservation is a form of deception which is not an outright lie. It was argued for in moral theology, and now in ethics, as a way to fulfill obligations both to tell the truth and to keep secrets from those not entitled to know them (for example, because of the seal of the confessional or other clauses of confidentiality). Mental reservation, however, is regarded as unjustifiable without grave reason for withholding the truth. This condition was necessary to preserve a general idea of truth in social relations.
In wide mental reservation, equivocations and amphibologies are used to imply an untruth that is not actually stated. In strict mental reservation, the speaker mentally adds some qualification to the words which he utters, and the words together with the mental qualification make a true assertion in accordance with fact.
A frequently cited example of equivocation is a well-known incident from the life of Athanasius of Alexandria. When Julian the Apostate was seeking Athanasius's death, Athanasius fled Alexandria and was pursued up the Nile. Seeing the imperial officers were gaining on him, Athanasius took advantage of a bend in the river that hid his boat from its pursuers and ordered his boat turned around. When the two boats crossed paths, the Roman officers shouted out, asking if anyone had seen Athanasius. One of Athanasius's followers shouted back, as instructed by Athanasius, "Yes, he is not very far off." The pursuing boat hastily continued up the river, while Athanasius returned to Alexandria, where he remained in hiding until the end of the persecution.
Another anecdote often used to illustrate equivocation concerns Francis of Assisi. He once saw a man fleeing from a murderer. When the murderer then came upon Francis, he demanded to know if his quarry had passed that way. Francis answered, "He did not pass this way," sliding his forefinger into the sleeve of his cassock, thus misleading the murderer and saving a life. A variant of this anecdote is cited by the canonist Martin de Azpilcueta to illustrate his doctrine of a mixed speech (oratoria mixta) combining speech and gestural communication.
Mentalis restrictio in moral theology 
The 16th-century Spanish theologian Martin de Azpilcueta (often called "Navarrus" because he was born in the Kingdom of Navarre) wrote at length about the doctrine of mentalis restrictio or mental reservation. Navarrus held that mental reservation involved truths "expressed partly in speech and partly in the mind," relying upon the idea that God hears what is in one's mind while human beings hear only what one speaks. Therefore the Christian's moral duty was to tell the truth to God. Reserving some of that truth from the ears of human hearers was moral if it served a greater good. This is the doctrine of strict mental reservation. A user of the doctrine could reply "I know not" aloud to a human interlocutor, and "to tell you" silently to God, and still be telling the truth (stricte mentalis).
Traditionally, the doctrine of mental reservation was intimately linked with the concept of equivocation, which allowed the speaker to employ double meanings of words to tell the literal truth while concealing a deeper meaning. Navarrus, however, went beyond this, giving the doctrine of mental reservation a far more broad and liberal interpretation than had anyone up to that time. Although some other Catholic theological thinkers and writers took up the argument in favor of strict mental reservation, the concept remained controversial within the Roman Catholic Church, which never officially endorsed or upheld the doctrine and eventually condemned it.
The linked doctrines of mental reservation and equivocation became notorious in England during the Elizabethan era and the Jacobean era, when Jesuits who had entered England to minister to the spiritual needs of Catholics were captured by the authorities. The Jesuits Robert Southwell (c. 1561–1595) (who was also a poet of note) and Henry Garnet (1555–1606) both wrote treatises on the topic, which was of far more than academic interest to them. Both risked their lives bringing the sacraments to recusant Catholics — and not only their lives, since sheltering a priest was a capital offence. In 1586, Margaret Clitherow had been pressed to death for refusing to enter a plea on the charge of harbouring two priests at York. When caught, tortured and interrogated, Southwell and Garnet practiced mental reservation not to save themselves — their deaths were a foregone conclusion — but to protect their fellow believers.
Southwell, who was arrested in 1592, was accused at his trial of having told a witness that even if she was forced by the authorities to swear under oath, it was permissible to lie to conceal the whereabouts of a priest. Southwell replied that that was not what he had said. He had said that "to an oath were required justice, judgement and truth", but the rest of his answer goes unrecorded because one of the judges angrily shouted him down. Convicted in 1595, Southwell was hanged, drawn and quartered. More famous in his own era was Henry Garnet, who wrote a defense of Southwell in 1598; Garnet was captured by the authorities in 1606 due to his alleged involvement in the Gunpowder Plot. Facing the same accusations as Southwell, his attempts to defend himself met with no better result: later that year Garnet was executed in the same fashion.
The Protestants considered these doctrines as mere justifications for lies. Catholic ethicists also voiced objections: the Jansenist "Blaise Pascal...attacked the Jesuits in the seventeenth century for what he saw as their moral laxity." "By 1679, the doctrine of strict mental reservation put forward by Navarrus had become such a scandal that Pope Innocent XI officially condemned it." Other casuists justifying mental reservation included Thomas Sanchez, who was criticized by Pascal in his Provincial Letters — although Sanchez added various restrictions (it should not be used in ordinary circumstances, when one is interrogated by competent magistrates, when a creed is requested, even for heretics, etc.), which were ignored by Pascal. Of the 26 theses condemned by Pope Innocent XI, several were in Sanchez's works (see op. mor. in præc. Decalogi, III, vi, n. 15). One of them stated:
|“||If anyone, by himself, or before others, whether under examination or of his own accord, whether for amusement or for any other purpose, should swear that he has not done something which he has really done, having in mind something else which he has not done, or some way of doing it other than the way he employed, or anything else that is true: he does not lie nor perjure himself.||”|
|“||Faith, here's an equivocator, that could swear in both the scales against either scale; who committed treason enough for God's sake, yet could not equivocate to heaven. (Macbeth, Act 2, Scene 3)||”|
Following Innocent XI's condemnation of strict mental reservation, equivocation (or wide mental reservation) was still considered orthodox, and was revived and defended by Alphonsus Liguori. The Jesuit Gabriel Daniel wrote in 1694 Entretiens de Cleanthe et d'Eudoxe sur les lettres provinciales, a reply to Pascal's Provincial Letters in which he accused Pascal of lying, or even of having himself used mental reservation, by not mentioning all the restrictions imposed by Sanchez on the use of this form of deception.
Kant and Constant 
This type of untruth was condemned by Kant in On a supposed 'right to lie’. Kant was debating against Benjamin Constant, who had claimed, from a consequentialist stance opposed to Kant's categorical imperative, that:
|“||To tell the truth is thus a duty; but it is only in respect to one who has a right to the truth. But no one has a right to a truth which injures others.||”|
On the other hand, Kant asserted, in the Groundwork of the Metaphysic of Morals, that lying, or deception of any kind, would be forbidden under any interpretation and in any circumstance. In Groundwork, Kant gives the example of a person who seeks to borrow money without intending to pay it back. The maxim of this action, says Kant, results in a contradiction in conceivability (and thus contradicts perfect duty) because it would logically contradict the reliability of language. If it is universally acceptable to lie, then no one would believe anyone and all truths would be assumed to be lies (this last clause was accepted by casuists, hence the reasons for restrictions given to the cases where deception was authorized). The right to deceive could also not be claimed because it would deny the status of the person deceived as an end in himself. And the theft would be incompatible with a possible kingdom of ends. Therefore, Kant denied the right to lie or deceive for any reason, regardless of context or anticipated consequences. However, it was permissible to remain silent or say no more than needed (such as in the infamous example of a murderer asking to know where someone is).
The doctrines have also been criticized by Sissela Bok and by Paul Ekman, who defines lies by omission as the main form of lying — though larger and more complex moral and ethical issues of lying and truth-telling extend far beyond these specific doctrines. Ekman, however, does not consider cases of deception where "it is improper to question" the truth as real form of deceptions — this sort of case, where communication of truth is not to be expected and so deception is justified, was included by casuists.
Social psychologists have advanced cases where the actor is confronted with an avoidance-avoidance conflict, in which he both doesn't want to say the truth and doesn't want to make an outright lie; in such circumstances, equivocal statements are generally preferred. This type of equivocation has been defined as “nonstraightforward communication...ambiguous, contradictory, tangential, obscure or even evasive.” People typically equivocate when posed a question to which all of the possible replies have potentially negative consequences, yet a reply is still expected (the situational theory of communicative conflict).
In Ireland 
The Irish Catholic Church allegedly misused the concept of mental reservation when dealing with situations relating to clerical child sexual abuse, by disregarding the restrictions placed on its employment by moral theologians and treating it as a method that "allows clerics (to) mislead people...without being guilty of lying", for example when dealing with the police, victims, civil authorities and media. In the Murphy Report into the Sexual abuse scandal in the Catholic archdiocese of Dublin, Cardinal Desmond Connell describes it thus:
|“||Well, the general teaching about mental reservation is that you are not permitted to tell a lie. On the other hand, you may be put in a position where you have to answer, and there may be circumstances in which you can use an ambiguous expression realising that the person who you are talking to will accept an untrue version of whatever it may be – permitting that to happen, not willing that it happened, that would be lying. It really is a matter of trying to deal with extraordinarily difficult matters that may arise in social relations where people may ask questions that you simply cannot answer. Everybody knows that this kind of thing is liable to happen. So mental reservation is, in a sense, a way of answering without lying.||”|
Cathleen Kaveny, writing in the Catholic magazine Commonweal, notes that Henry Garnet in his treatise on the topic took pains to argue that no form of mental reservation was justified — and might even be a mortal sin — if it would run contrary to the requirements of faith, charity or justice. But according to the Murphy Report:
|“||The Dublin Archdiocese's preoccupations in dealing with cases of child sexual abuse, at least until the mid 1990s, were the maintenance of secrecy, the avoidance of scandal, the protection of the reputation of the church, and the preservation of its assets. All other considerations, including the welfare of children and justice for victims, were subordinated to these priorities. The archdiocese did not implement its own canon-law rules and did its best to avoid any application of the law of the state.||”|
Kaveny concludes: "The truths of faith are illuminated by the lives of the martyrs. Southwell and Garnet practiced mental reservation to save innocent victims while sacrificing themselves. The Irish prelates practiced mental reservation to save themselves while sacrificing innocent victims. And that difference makes all the difference."
See also 
- John Henry Newman. Apologia pro Vita Sua, Note G: Lying and Equivocation.
- Zagorin, p. 15.
- Martin de Azpilcueta Azpilcueta, Martin, (Navarra), Commentarius in cap. Humanae Aures, XXII. qu. V. De veritate responsi; partim verbo expresso, partim mente concepti. & de arte bona & mala simulandi, Roma, 1584. Quoted by J.-P. Cavaillé, Ruser sans mentir, de la casuistique aux sciences sociales : le recours à l’équivocité, entre efficacité pragmatique et souci éthique, published in Serge Latouche, P.-J. Laurent, O. Servais & M. Singleton, Les Raisons de la ruse. Une perspective anthropologique et psychanalytique, Actes du colloque international « La raison rusée », Louvain la Neuve, mars 2001, Paris, La Découverte, 2004, p. 93–118 (French)
- Cathleen Kaveny. "Truth or Consequences: In Ireland, Straying Far from the Mental Reservation". Commonweal, January 15, 2010.
- Margaret Clitherow Shrine, York.
- Fiorella Sultana De Maria. Robert Southwell. London: CTS, 2003, p. 49.
- Randal, p. 151.
- Brown, p. 41.
- Matthew Stapleton, "Is Kantian Ethics Left Defenseless in the Face of Evil?"
- J.-P. Cavaillé, Ruser sans mentir, de la casuistique aux sciences sociales : le recours à l’équivocité, entre efficacité pragmatique et souci éthique, published in Serge Latouche, P.-J. Laurent, O. Servais & M. Singleton, Les Raisons de la ruse. Une perspective anthropologique et psychanalytique, Actes du colloque international « La raison rusée », Louvain la Neuve, mars 2001, Paris, La Découverte, 2004, p. 93–118 (French).
- Bok, pp. 35–7 and ff.
- Paul Ekman, Why Don't We Catch Liars?
- Janet Beavin Bavelas, Alex Black, Nicole Chovil, and Jennifer Mullet, Equivocal Communications, Newbury Park, CA, Sage Publications, 1990.
- Bavelas et al., p. 28.
- See also Peter Bull, Equivocation and Facework in the Discourse of Televised Political Interviews.
- "Church 'lied without lying'", The Irish Times, 11 November 2009.
- Bok, Sissela. Lying: Moral Choice in Public and Private Life. New York, Vintage, 1978.
- Brown, Meg Lota. Donne and the Politics of Conscience in Early Modern England. Boston, Brill Academic Publishers, 1995.
- Leites, Edmund, ed. Conscience and Casuistry in Early Modern Europe. Cambridge, Cambridge University Press, 1988.
- Randal, Marlin. Propaganda and the Ethics of Persuasion. Orchard Park, NY, Broadview Press, 2002.
- Zagorin, Perez. "The Historical Significance of Lying and Dissimulation: Truth-Telling, Lying and Self-Deception". Social Research, Fall 1996.