RESERVATION, MENTAL: A secret mental restriction or repression in thought, an offense against the duty of truthfulness by which a part of the truth is concealed, and so an intentional deceit prepared. It may refer either to the past or the future; to the statement of what is alleged to have happened or to be at hand, or to an assurance of something to be rendered or kept. The assertory as well as the promissory oath can thus give occasion to its commission. It may also occur in daily social intercourse. Mental reservation plays a considerable role in the lax moral system of the Jesuits. Many of their authors as well as some Roman Catholic moralists outside supported the use of this reservation. Among the former J. Caramuel was the most thorough-going in his Haplotes de restrictionibus mentalibus (Leyden, 1672). Antoninus Diana (d. 1663) taught that "if anyone voluntarily offers to take an oath, by necessity or for some utility, he may use double meanings, for he has a just ground for using them" (Resolutiones morales, II., tract 15, 25-26, III., tract 5, 100 and 6, 30). So if anyone requests a loan from another which the other can not give, he may say that he does not have it, reserving the mental addition, in order to loan it to him. If one is asked about a crime of which he is the only witness, he can say that he does not know it, adding mentally, as an openly known crime. On proper grounds, an ambiguous oath does not involve perjury, if, without change of form, the ambiguous sense may be produced; one does not need to confess to a committed offense before a court, if thereby an injury to self is invited; one can deny having committed it, with the reservation in mind, "in prison." Knowingly to lead any one to take a false oath is no sin because the person who takes the oath is knowingly doing no evil; and to swear falsely from habit is a pardonable sin. For numerous parallel instances of the older and later moralists cf. Count P. von Hoensbroech, Das Papsttum, vol. ii., Die ultramontane Moral, pp. 223 sqq. (Leipsic, 1902), among which occur the scandalous example from J. P. Gury's Casus conscienti (Lyons, 1864) of Anna the adulteress, and the author's own citation from the Roman Analecta ecclesiastica of June, 1901; both of which cases involve an equivocating denial of an offense after absolution.
Protests against the system of mental reservation are found not only among Protestants of all classes, but the more serious Roman Catholic theology either defined it more or less closely or else condemned it positively; as, for example, the author on moral theology, G. V. Pautuzzi (d. 1679), Ethica Christiana (Venice, 1770). The methods of modern Jesuit moralists are said to be wholly subservient to the apology and justification of moral restrictions. A. Lehmkuhl (KL, x. 1082-89) represents, as the only correct view, that which asserts that cases may arise in which a restrictio late mentalis, or external reservation or ambiguous statement, may be employed. In such cases the one speaking does not deceive so much as the one arriving at an erroneous judgment deceives himself. In such cases where the reservation is permissible, if the matter is of sufficient importance, the statement may be reenforced by oath without committing perjury. See JESUITS, II., § 6.