Definition

(Summa Theologica, I, q. 79, aa. 11-13.)

Definition.—Conscience is an act of judgment on the part of the practical reason deciding by inference from general principles the moral goodness or malice of a particular act.

(a) It is an act, and as such it differs from moral knowledge and intellectual virtues, which are not transitory but enduring. Moral understanding (synderesis), by which everyone naturally perceives the truth of general and self-evident principles of morality; moral science, by which the theologian or ethician knows the body of conclusions drawn from moral principles; prudence, by which the virtuous man is able to make right applications of moral rules to individual cases—all these are permanent states and are preparatory to the act of conscience, in which one makes use of one’s knowledge to judge of the lawfulness or unlawfulness of an action in the concrete, as attended by all its circumstances.

(b) Conscience is an act of judgment, and thus it differs from the other acts employed by prudence—from counsel about the right means or ways of action, and from command as to their use. Counsel inquires what is the right thing to do, conscience gives the dictate or decision, the moral command moves to action.

(c) Conscience is in the reason—that is, it is a subjective guide, and thus it differs from law, which is objective.

(d) Conscience is in the practical reason. Unlike other judgments, which are speculative and deal not with action or only with theoretical aspects of action (e.g., the judgment that God is perfect, that the active faculties are distinct from the soul, etc.), conscience is concerned with action from the view-point of its moral exercise.

(e) Conscience is the inference from general principles, and thus it differs from moral understanding (synderesis). This latter is a habit by which everyone who is mentally developed is able to perceive without argument that certain more general propositions of morality must be true, such as the axioms of the natural law (see above, 319 sqq.); conscience draws conclusions from those axioms.

(f) Conscience judges concerning the morality of an act. Here lies the difference between consciousness and conscience; consciousness is a psychological faculty whose function is to perceive one’s own states and acts; conscience is a moral judgment concerning the lawfulness or unlawfulness of those states or acts. Thus, consciousness testifies that one is considering the performance of a certain act, conscience judges the morality, and permits or forbids; or consciousness testifies that a certain thing was done or not done in the past, conscience declares the morality—condemning, excusing, or approving what took place.

(g) Conscience judges concerning a particular act—that is, it considers an act that is to be done here and now (or was done), with all the attendant circumstances. Conscience, thus, differs from moral science, which, though it systematizes the body of conclusions drawn from the natural and positive laws, is not able to make the applications for the innumerable cases that arise. Even works containing moral cases, which give solutions for concrete instances, do not take the place of conscience in such instances, for it is still the individual who judges about those solutions or about their applicability to his particular circumstances.