Reservation, MENTAL (Lat. reservatio or restrictio mentalis), the act of reserving or holding back some word or clause which is necessary to convey fully the meaning really intended by the speaker. It differs from equivocation (Lat. equivocatio or amphibolia) in this, that in the latter the words employed, although doubtful, and perhaps not fitted naturally to convey the real meaning of the speaker, are yet, absolutely speaking, and without the addition of any further word or clause, susceptible of that meaning. Few questions in casuistry have excited more controversy, or have been the subject of fiercer recrimination, than that of the lawfulness of equivocation and mental reservation. In the celebrated Letters of Pascal (q.v.) against the Jesuits it was one of the most prominent and, used as he employed it, the most effective topics; and Pascal's charges against the Jesuit casuistry of that day have been repeated in almost every popular controversy on the subject which has since arisen. There are several varieties of mental reservation, differing from each other, and all differing from equivocation. But as regards the morality of the subject all the forms of language calculated to deceive may be classed together. Mental reservation is of two kinds, purely mental and not purely mental. By the former designation is meant a mental reservation which cannot be detected, whether in the words themselves, or in the circumstances in which they are spoken. Of this kind would be the mental reservation implied if a person, on being asked if he had seen A. B. (whom he really had just seen walking by), were to reply: 'I have not seen him,' meaning 'riding on horseback.' A 'not purely mental' reservation is that which, although not naturally implied or contained in the words, may nevertheless be inferred or suspected, either from them or the circumstances in which they are used. Of this kind would be the mental reservation of a servant, in giving the ordinary answer to a visitor's inquiry for his master: 'Not at home,' although his master were really in the house; or that of a confessor, who, in a country where the privileges of the secret of the confessional are known and admitted, on being asked whether a certain person had committed a crime, which the confessor knew from his confession that he had committed, should answer: 'I do not know,' meaning 'outside of the confessional.' And, in general, all such doubtful forms, whether of mental reservation or of equivocation, may be divided into discoverable and undiscoverable. Much of the odium which has been excited against the casuists for their teaching on this head has arisen from the confusion of their views as to these two classes of mental reservation.
According to the most approved Catholic authorities, 'purely mental' reservations and 'absolutely undiscoverable' equivocations are held to be in all cases unlawful, such forms of speech being in truth lies, inasmuch as they have but one real sense, which is not the sense intended by the person who uses them, and hence can only serve to deceive. This doctrine is held by all sound Catholic casuists, and the contradictory doctrine is expressly condemned by Pope Innocent XI. (Propp. 26, 27). On the contrary, mental reservations 'not purely mental' and 'discoverable' equivocations are held to be not inconsistent with truth, and in certain circumstances, when there is necessity or weighty reason for resorting to them, allowable. An historical example of such equivocation or reservation is in the well-known answer of St Athanasius to the question of the party who were in pursuit of him, and who, overtaking him, but not knowing his person, asked what way Athanasius had gone. 'He is not far off,' replied Athanasius, and the party passed on in pursuit. And an ordinary example of discoverable mental reservation is that of a person who, on being asked by one to whom he could not with safety give a refusal, whether he has any money, should reply: 'No,' meaning, 'none to lend to you.' In order, however, to justify the use of these devices of speech, casuists require that there shall be some grave and urgent reason on the speaker's part; as, for example, the necessity of keeping a state secret, or a secret of the confessional, or of a professional character, or even the confidence entrusted by a friend, or the ordinary and fitting privacy which is required for the comfort and security of domestic life and of the peaceful intercourse of society; and that the concealed sense of the form of speech employed, although it may be actually undiscovered, and even unlikely to be discovered, may yet be, in all the circumstances, really discoverable. Some Protestant moralists admit that in some cases even equivocation is permissible; if any such reservations are allowed it is obvious there must be great difficulty in drawing a line between reservations that are permissible and those that are not. See CASUISTRY; Liguori's works; and Cardinal Newman's Apologia.