Chapter I: On the Force of Certain Conscience

— Practically certain conscience is always to be followed. Wherefore whether it be speculatively true or erroneous, the action will in reality have the goodness or malice which conscience proposes.

This is clear from Genesis 20, 4-7, where the excuse of his ignorance which Abimelech alleged is approved by God, and from the passage of the Apostle, Rom. 14, 14. 22. 23, compared with 1 Cor. 8, 11, where St. Paul teaches that conscience is polluted because of an action which is falsely thought illicit. And the reason is, because by the will by which a Superior wills something to be observed, by the same will he wills that obedience be given to the one herald, designated by him and faithful of himself, through whom alone his commands are intimated. But conscience performs the function of such a herald. For the rest, since the object of the will is the action as it is proposed by the intellect, the act receives its species from the object, "not according to the matter of the object but according to the account of the object" (St. Th. Quodl. 3, art. 27).

Wherefore the sin committed against a right conscience and the sin committed against an erroneous conscience do not differ in species.

Yet the act must always be supposed human. Wherefore involuntary distractions will not be imputed to him who erroneously thinks those same things to be sins.

— What if the conscience of ignorance or error has been culpable?

If while acting, the unskilled man does not advert to his ignorance, he has an actually invincible conscience, which by following he cannot actually sin. Yet he will bear the consequences of the harmful action, if any were sufficiently foreseen in the prior fault.

If while acting he was mindful of his ignorance, he ought to have inquired concerning the matter or abstained from the action.

Yet what if the action is necessary and the opportunity of inquiring is lacking: suppose an ignorant priest, who alone comes upon a sick man for whom death is imminent. Then his ignorance is reduced to invincible, nor will the error be imputed to him, unless, from the office which he bears, he could easily have foreseen that these circumstances would occur.

If, with inquiry omitted, he does not abstain from the action, the ignorant man will sin whether he acts according to or against the dictate of his conscience. And by acting according to the dictate, he will sin by his negligence and will be guilty of the evils which he foresaw confusedly. But by acting against conscience, he will besides sin by the sin apprehended through actual conscience.

A vincibly or invincibly erroneous conscience will be judged both from the presumptions which the matter and the person permit (with attention paid to his piety and learning), and from fitting interrogations of the agent: a) whether he adverted to any indecency in the act; b) whether he doubted concerning the liceity of the action; c) whether conscience warned him concerning a grave or light obligation of inquiring.

— Practically certain conscience is always to be followed, with the imputation of error culpable in its cause nevertheless saved. Even one guilty of conscious negligence will sin more by acting against conscience commanding or forbidding than according to it. But a vincibly or invincibly erroneous conscience must be prudently estimated.