SYNDERESIS. - A medieval term equivalent to the "moral sense" of the moderns, understood as "the spiritual quality by which we know the first principles of the practical order, regulators of all practical knowledge" (Y. Simon, Critique de la connaissance morale, Paris 1934, p. 56). Synderesis is therefore distinguished, although it is its ultimate root, from "moral conscience" (συνείδησις).
The term seems to derive from συνενηρέα, I look attentively, I observe, and was used by the Stoics; but it is doubtful whether they saw a difference in meaning between συνενηρέσεις and συνείδησις (cf. M. Waldmann, Synteresis oder Synedesis? Ein Beitrag zur Lehre vom Gewissen, in Theol. Quartalschr., 109 [1938], p. 323 ff.). It passed into scholasticism through a text of St. Jerome, who above the three faculties of the soul (rational, irascible, concupiscible) places a fourth "quam Graeci vocant συνενηρεσιν, quae scintilla conscientiæ in Cain quoque pectore, postquam eiectus est de paradiso, non extinguitur, et qua victi voluptatibus vel furore, ipsaque interdum rationis decepti similitudine, nos peccare sentimus... Et tamen hanc quoque conscientiam... cernimus praecipitari apud quosdam et suum locum ammittere... " (Comm. in Ezech., I, cap. 1: PL 25, 22). Among the scholastics the term is already found in Magister Udo, in his commentary (ca. 1160) on Peter Lombard, who had first examined the text of St. Jerome (Libri IV sententiarum, II, dist. 39, at the end). Variously studied and interpreted in the 12th and 13th centuries, synderesis found its two fundamental interpretations in the work of St. Bonaventure and St. Thomas. St. Bonaventure (In II Sent., dist. 39, aa. 1-2) considers synderesis as "potentiam effectivam inquantum naturaliter habilis est ad bonum et ad bonum tendit", that is, the natural will itself, insofar as it is inclined to the moral good; it is therefore distinguished from conscience, which is "naturale iudiciatorium, dirigens ipsum intellectum in conoscendis". St. Thomas, on the other hand (In II Sent., dist. 24, q. 2, aa. 3-4; dist. 39, q. 3, a. 1; De verit., q. 16; Sum. Theol., 1ª, q. 79, aa. 12-13; 1ª-2ª, q. 94, a. 1; 2ª-2ª, q. 47, a. 6) places synderesis on the plane of practical knowledge, as a natural intellectual habit of the first principles directing human activity.
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Tullio Piacentini