[A]s the first principles of speculative reason, synderesis, the habit of practical reason, cannot be lost. (…) Strictly speaking, conscience is concerned with the conclusion of a practical syllogism. It is therefore the application of first and universal principles (of which synderesis is the habit) to a particular situation. In this syllogism, synderesis provides the major term, as the following example illustrates:
- Evil must always be avoided (a first principle grasped by synderesis).
- Adultery is evil (forbidden by God).
- Therefore, the act of adultery must be avoided (application of a judgment of conscience).
Conscience is a norm closer to morality, subordinated to synderesis through a conclusion derived from the premises; therefore, conscience is an act. The error is not in the major term (synderesis), but in the defective practical syllogism and means that the conclusion (conscience) is false. This is St Thomas’s interpretation of St Jerome’s commentary on Ezekiel 1 which states that synderesis can be cast into the abyss. For St Thomas, this refers to conscience rather than synderesis. (…)
‘Being cast off into the abyss’ is not a quality of synderesis on the universal level. Error can occur when a universal principle is applied to a particular situation because of either an argument’s vice or its falsehood. This is why the text states that conscience can be wrong. Conscience applies the universal judgment of synderesis to particular situations. (…)
[Synderesis] is the light of knowledge of good and evil, which is natural and innate, that inclines towards good and opposes evil. In this perspective, it is insufficient to argue that synderesis is impeccable. Its primary qualities are rather inerrancy and infallibility. (…)
Despite the outdated nature of the term synderesis, the Thomist approach to the reality it designates is close to how Newman’s Letter to the Duke of Norfolk and the pastoral constitution Gaudium et spes (§16) understand conscience. Thomas’s approach emphasises the unchanging dignity of the human person and his or her ineluctable responsibility. The inner voice that approves good and opposes evil is the inner eye that the first murderer cannot flee. Victor Hugo immortalised this in the last alexandrine of his famous poem, ‘l’oeil était dans la tombe et regardait Caïn’. This voice is no less a treasure that forbids despairing over any sinner who still has the breath of life.
Somme, Luc-Thomas, OP, “The Infallibility, Impeccability and Indestructibility of Synderesis.” Omsett av Katherine Shirk (Studies in Christian Ethics 19.3 (2006), s. 403–416. Her s. 406-407.416 (Side 5-6.15 i pdf-utgåva) (27.08.2007)