Today’s Catechism sections discuss man’s conscience. Supporting material comes from the “Summa Theologica”.

Article 6

MORAL CONSCIENCE

1776 "Deep within his conscience man discovers a law which he has not laid upon himself but which he must obey. Its voice, ever calling him to love and to do what is good and to avoid evil, sounds in his heart at the right moment.... For man has in his heart a law inscribed by God.... His conscience is man's most secret core and his sanctuary. There he is alone with God whose voice echoes in his depths."47

I. The Judgment of Conscience

1777 Moral conscience,48 present at the heart of the person, enjoins him at the appropriate moment to do good and to avoid evil. It also judges particular choices, approving those that are good and denouncing those that are evil.49 It bears witness to the authority of truth in reference to the supreme Good to which the human person is drawn, and it welcomes the commandments. When he listens to his conscience, the prudent man can hear God speaking.

1778 Conscience is a judgment of reason whereby the human person recognizes the moral quality of a concrete act that he is going to perform, is in the process of performing, or has already completed. In all he says and does, man is obliged to follow faithfully what he knows to be just and right. It is by the judgment of his conscience that man perceives and recognizes the prescriptions of the divine law:

Conscience is a law of the mind; yet [Christians] would not grant that it is nothing more; I mean that it was not a dictate, nor conveyed the notion of responsibility, of duty, of a threat and a promise.... [Conscience] is a messenger of him, who, both in nature and in grace, speaks to us behind a veil, and teaches and rules us by his representatives. Conscience is the aboriginal Vicar of Christ.50

1779 It is important for every person to be sufficiently present to himself in order to hear and follow the voice of his conscience. This requirement of interiority is all the more necessary as life often distracts us from any reflection, self-examination or introspection:

Return to your conscience, question it.... Turn inward, brethren, and in everything you do, see God as your witness.51

1780 The dignity of the human person implies and requires uprightness of moral conscience. Conscience includes the perception of the principles of morality (synderesis); their application in the given circumstances by practical discernment of reasons and goods; and finally judgment about concrete acts yet to be performed or already performed. The truth about the moral good, stated in the law of reason, is recognized practically and concretely by the prudent judgment of conscience. We call that man prudent who chooses in conformity with this judgment.

1781 Conscience enables one to assume responsibility for the acts performed. If man commits evil, the just judgment of conscience can remain within him as the witness to the universal truth of the good, at the same time as the evil of his particular choice. The verdict of the judgment of conscience remains a pledge of hope and mercy. In attesting to the fault committed, it calls to mind the forgiveness that must be asked, the good that must still be practiced, and the virtue that must be constantly cultivated with the grace of God:

We shall . . . reassure our hearts before him whenever our hearts condemn us; for God is greater than our hearts, and he knows everything.52

1782 Man has the right to act in conscience and in freedom so as personally to make moral decisions. "He must not be forced to act contrary to his conscience. Nor must he be prevented from acting according to his conscience, especially in religious matters."53

In the “Summa Theologica” (1, 79, 13), St. Thomas Aquinas discusses the conscience.

Article 13. Whether conscience be a power?

Objection 1. It would seem that conscience is a power; for Origen says [Commentary on Romans 2:15] that "conscience is a correcting and guiding spirit accompanying the soul, by which it is led away from evil and made to cling to good." But in the soul, spirit designates a power--either the mind itself, according to the text (Ephesians 4:13), "Be ye renewed in the spirit of your mind"--or the imagination, whence imaginary vision is called spiritual, as Augustine says (Gen. ad lit. xii, 7,24). Therefore conscience is a power.

Objection 2. Further, nothing is a subject of sin, except a power of the soul. But conscience is a subject of sin; for it is said of some that "their mind and conscience are defiled" (Titus 1:15). Therefore it seems that conscience is a power.

Objection 3. Further, conscience must of necessity be either an act, a habit, or a power. But it is not an act; for thus it would not always exist in man. Nor is it a habit; for conscience is not one thing but many, since we are directed in our actions by many habits of knowledge. Therefore conscience is a power.

On the contrary, Conscience can be laid aside. But a power cannot be laid aside. Therefore conscience is not a power.

I answer that, Properly speaking, conscience is not a power, but an act. This is evident both from the very name and from those things which in the common way of speaking are attributed to conscience. For conscience, according to the very nature of the word, implies the relation of knowledge to something: for conscience may be resolved into "cum alio scientia," i.e. knowledge applied to an individual case. But the application of knowledge to something is done by some act. Wherefore from this explanation of the name it is clear that conscience is an act.

The same is manifest from those things which are attributed to conscience. For conscience is said to witness, to bind, or incite, and also to accuse, torment, or rebuke. And all these follow the application of knowledge or science to what we do: which application is made in three ways. One way in so far as we recognize that we have done or not done something; "Thy conscience knoweth that thou hast often spoken evil of others" (Ecclesiastes 7:23), and according to this, conscience is said to witness. In another way, so far as through the conscience we judge that something should be done or not done; and in this sense, conscience is said to incite or to bind. In the third way, so far as by conscience we judge that something done is well done or ill done, and in this sense conscience is said to excuse, accuse, or torment. Now, it is clear that all these things follow the actual application of knowledge to what we do. Wherefore, properly speaking, conscience denominates an act. But since habit is a principle of act, sometimes the name conscience is given to the first natural habit--namely, "synderesis": thus Jerome calls "synderesis" conscience (Gloss. Ezekiel 1:6); Basil [Hom. in princ. Proverb.], the "natural power of judgment," and Damascene [De Fide Orth. iv. 22 says that it is the "law of our intellect." For it is customary for causes and effects to be called after one another.

Reply to Objection 1. Conscience is called a spirit, so far as spirit is the same as mind; because conscience is a certain pronouncement of the mind.

Reply to Objection 2. The conscience is said to be defiled, not as a subject, but as the thing known is in knowledge; so far as someone knows he is defiled.

Reply to Objection 3. Although an act does not always remain in itself, yet it always remains in its cause, which is power and habit. Now all the habits by which conscience is formed, although many, nevertheless have their efficacy from one first habit, the habit of first principles, which is called "synderesis". And for this special reason, this habit is sometimes called conscience, as we have said above.

Footnotes

47 GS 16.
48 Cf. ⇒ Rom 2:14-16.
49 Cf. ⇒ Rom 1:32.
50 John Henry Cardinal Newman, "Letter to the Duke of Norfolk," V, in Certain Difficulties felt by Anglicans in Catholic Teaching II (London: Longmans Green, 1885), 248.
51 St. Augustine, In ep Jo. 8, 9: PL 35, 2041.
52 1 ⇒ Jn 3:19-20.
53 DH 3 # 2.