De veritate EN 150



Some say that conscience can have three meanings. For, at limes it is taken for the thing itself of which one is conscious, just as faith is taken for the thing believed. Sometimes it is taken for the power by which we are conscious, and sometimes for the habit. And some say that it is also taken for the act. The reason for this distinction seems to be that, since there is an act of conscience, and since an object, a power, a habit, and the act itself are considered will reference to the act, we sometimes find a name which is used equivocally for all four of these. Thus, the name understanding sometimes signifies the thing understood (intellectam), as names are said to denote concepts (intellectus); sometimes, it signifies the intellective power itself; sometimes, a habit, and, sometimes, an act.

However, will names such as these, the commonly accepted meaning should be followed, because words should be used in their more common signification, as is said in the Topics. But the name conscience, according to common usage, seems at times to be used for the thing of which one is conscious, as when one says: "I will reveal my conscience to you," that is, what is in my conscience. But this title cannot properly be given to the power or the habit, but only to the act. For all the things which are attributed to conscience fit only this meaning.

We must bear in mind that it is not customary to have one name for a power, an act, and a habit, unless the act is proper to the power or habit, as to see is proper to the power of sight, and to know is proper to the habit of knowledge. As a result, sight sometimes means the power and sometimes the act. Knowledge is used in a similar way. However, if there is an act which is proper to many or all habits or powers, it is not customary to indicate a power or a habit by such a name of the act. This is clear will the noun use, for it denotes the act of any habit and power, since use belongs to that of which it is the act. Hence, this name use so signifies an act that it does not mean a habit or a power at all.

This seems to be the case will conscience. For the name conscience means the application of knowledge to something. Hence, to be conscious (conscire)means to know together (simul scire). But any knowledge can be applied to a thing. Hence, conscience cannot denote a special habit or power, but designates the act itself, which is the application of any habit or of any knowledge w some particular act.

Moreover, knowledge is applied to an act in two ways. According to one way, we consider whether the act exists or has existed; according to the other, whether it is correct or not. According to the first mode of application, we are said to have conscience [that is consciousness], of an act inasmuch as we know that the act has been placed or has not been placed, as happens in the common manner of speaking when one says: "As far as my conscience [consciousness] is concerned, this has not taken place; that is, I do not know or I did not know whether this took place." It is according to this manner of speaking that we understand the passage in Genesis (43:22): "cannot tell [non est in conscientiis nostris] who put it (the money) in our bags"; and the passage in Ecclesiastes (7:23): "For thy con science knoweth that thou also hast often spoken evil of others." it is according to this that conscience is said to bear witness of some thing, as in Romans (9:1): "my conscience bearing me witness...

According to the second mode of application, by which knowledge is applied to an act, so that one knows whether the act is right or not, there is a double course. There is one according to which we are directed through the habit of scientific knowledge to do or not to do something. There is a second according w which the act, after it has taken place, is examined will reference w the habit of knowledge to see whether it was right or not. This double course in matters of action is distinguished according to the double course which exists in things speculative, that is, the process of discovery and the process of judging. For the process by which through scientific knowledge we look for what should be done, as it were taking counsel will our selves, is similar to discovery, through which we proceed from principles to conclusions. The other process, through which we examine those things which already have been done and consider whether they are right, is like the process of judging, through which we reduce conclusions w principles.

We use the name conscience for both of these modes of application. For, in so far as knowledge is applied to an act, as directive of that act, conscience is said to prod or urge or bind. But, in so far as knowledge is applied to act, by way of examining things which have already taken place, conscience is said w accuse or cause remorse, when that which has been done is found to be out of harmony will the knowledge according to which it is examined; or w defend or excuse, when that which has been done is found to have proceeded according to the form of the knowledge.

But we must bear in mind that in the first application, in which scientific knowledge is applied w an net to know whether it has taken place, it is application to a particular act of sensitive knowledge, as of memory, through which we recall what was done, or of sense, through which we perceive the particular act in which we are now engaged. But in the second and third applications, by which we deliberate about what should be done, or examine what has already been done, the operative habits of reason are applied to an act. These are the habit of synderesis and the habit of wisdom, which perfect higher reason, and the habit of scientific knowledge, which perfects lower reason of these, either all are applied at the same time, or only one of them is applied. We examine what we have done according to these habits, and, according to them, we take counsel about what should be done. Examination, however, concerns not only what has been done, but also what is to be done. But counsel concerns only what is to be done.

Answers to Difficulties (First Series):

1. When Jerome says: "We see that this conscience is cast down headlong at times," synderesis, which he calls a spark of conscience, is not indicated, but conscience itself, which he had mentioned earlier. Or we can say that the whole force of conscience, as examining or taking counsel, depends on the judgment of synderesis, just as the whole truth of speculative reason depends on first principles. There fore, he calls conscience synderesis in so far as conscience acts by reason of its power. This answer is especially apt because he wanted to show how synderesis can fail. For it does not err in regard to universal principles, but only in regard to the application to individual acts. Thus, synderesis does not err in itself, but, in a sense, errs in con science. Therefore, he joins conscience will synderesis to explain this failure of synderesis.

2. Defilement is not said to be in conscience as in a subject, but as the thing known is in knowledge. For one is said to have a defiled con science when he is conscious within himself of some defilement.

3. A defiled conscience is said to be cleansed, in so far as one who was earlier conscious of sin knows later that he has been cleansed from the sin. Thus, he is said to have a pure conscience. Accordingly, it is the same conscience which first was unclean and later clean, not, how ever, in the sense that conscience is the subject of cleanness and un cleanness, but that through examination made by conscience both are known. It is not that it is numerically the same act by which one knew he was unclean before and knows he is clean afterwards, but that both are known from the same principles, just as consideration which proceeds from the same principles is called the same.

4. The judgments of conscience and of free choice differ to some extent and correspond to some extent. For they correspond in this, that both refer to this particular act. However, the judgment of con science applies to it in so far as conscience examines it. On this point the judgment of both conscience and free choice differ from the judgment of synderesis. They differ from each other, since the judgment of conscience consists simply in knowledge, whereas the judgment of free choice consists in the application of knowledge to the inclination of the will. This is the judgment of choice.

Thus, it sometimes happens that the judgment of free choice goes astray, but not the judgment of conscience. For example, one debates something which presents itself to be done here and now and judges, still speculating as it were in the realm of principles, that it is evil, for instance, to fornicate will this woman. However, when he comes to apply this to the act, many circumstances relevant to the act present themselves from all sides, for instance, the pleasure of the fornication, by the desire of which reason is constrained, so that its dictates may not issue into choice. Thus, one errs in choice and not in conscience. Rather, he acts against conscience and is said to do this will an evil conscience, in so far as the deed does not agree will the judgment based on knowledge. Thus, it is clear that it is not necessary for con science to be the same as free choice.

5. Conscience is called the natural power of judgment in so far as the whole examination or counselling of conscience depends on the natural power of judgment, as we said earlier.

6. Sin is in the reason and the will as in a subject, but it is in con science in a different way, as has been said.

7. Conscience is said to know something not in a proper sense, but in the sense that knowledge is predicated of that by which we know.

8. Conscience is called spirit, that is, an impulse of our spirit, just as reason is called spirit.

9. Conscience is neither a power nor a habit, but an act. And, al though the act of conscience does not always exist, and does not exist in one who is asleep, the act itself remains in its principle, that is, in habits which can be applied to act.

Answers to Difficulties (Second Series):

1-6. We concede the difficulties which prove that conscience is not a habit.

Answers to Difficulties to the Contrary (First Series):

1'. Conscience is called the law of our understanding because it is a judgment of reason derived from the natural law.

2’. One is said to be conscious within himself through the natural law, in the sense in which one is said to deliberate according to principles, but he is conscious within himself through conscience, in the sense in which he is said to deliberate by means of the very act of consideration.

3’. Although scientific knowledge is a habit, its application to some thing is not a habit, but an act. And this is what is indicated by the word conscience.

4’. From these acts there does not arise a habit of a different mode from the habit by which the acts are elicited, but either a habit of the same nature is formed, as the habit of love is formed from acts of in fused charity, or an already present habit is strengthened, as in one who has acquired the habit of temperance from repeated acts, the habit itself is strengthened. Accordingly, since the act of conscience proceeds from a habit of wisdom and science, a new habit will not be formed from them, but those habits will be perfected.

5’. When conscience is called hope, the predication is causal in nature, inasmuch as a good conscience makes a man be of good hope, as the Gloss explains.

6’. Even natural habits exist in us because they were put there by God. Consequently, since conscience is an act proceeding from the natural habit of synderesis, God is said to have imprinted it in the way in which He is said to be the source of all knowledge of truth which is in us. For God endows our nature will the knowledge of first principles.

7’. Act is included in habit in that division of the Philosopher be cause he had proved that habits are formed from acts, and that habits were the principle of similar acts. Accordingly, conscience is not a passion nor a power, but an act, which is reduced to a habit.

Answers to Difficulties to the Contrary (Second Series):

We concede the difficulties which prove that conscience is an act.


Parallel readings: II Sentences 24, 2, 4; 39, 3, I, ad I; 3 3, 2; Quolibet III, 12, 26.


It seems that it cannot, for

1. The natural power of judgment is never mistaken. But, according to Basil, conscience is "the natural power of judgment." Therefore, it is not mistaken.

2. Conscience adds something to scientific knowledge. Moreover, that which it adds in no way detracts from the nature of scientific knowledge. But scientific knowledge is never mistaken, since it is the habit by which one always speaks the truth, as is clear in the Ethics. Therefore, neither can conscience be mistaken.

3. Synderesis is "a spark of conscience," as Jerome says. Therefore, conscience is related to synderesis as fire is to a spark. But the activity and movement of a fire and of a spark [from it] are the same. There fore, the activity and movement of conscience and synderesis are also the same. But synderesis is never mistaken. Therefore, neither is con science.

4. According to Damascene, conscience is the "law of our under standing." But the law of our understanding is more certain than the understanding itself, and, "understanding is always correct," as is said in The Soul. Therefore, will much greater reason, conscience is always correct.

5. Reason, in so far as it is coincident will synderesis, does not make mistakes. But reason joined to synderesis constitutes conscience. Therefore, conscience never makes mistakes.

6. The testimony of witnesses is decisive in court. But conscience is the witness in the divine court, as is clear from Romans (2: 5): "their conscience bearing witness to them." Therefore, since the divine court never can be deceived, it seems that conscience can never err.

7. In all things, the rule which regulates other things must be in fallibly correct. But conscience is a rule of human actions. Therefore, conscience must always be correct.

8. Hope depends on conscience, according to the Gloss on the first Epistle to Timothy (1: "From a pure heart, and a good con science..."But hope is most certain, according to Heb., "we have the most certain comfort, who have fled for refuge to hold fast the hope set before us." Therefore, conscience is infallibly correct.

To the Contrary:

1'. In John (16:2) we read: "The hour cometh, when whosoever killed you, will think that he doth a service to God." Therefore, their conscience told those who killed the Apostles that they would please God by this action. But this was a mistake. Therefore, conscience makes mistakes.

2’. Conscience includes comparison. But reason can be deceived when it makes comparisons. Therefore, conscience can make mistakes.



As is clear from what has been said, conscience is nothing but the application of knowledge to some special act. Error, however, can occur in this application in two ways; in one, because that which is applied has error within it, and, in the other, because the application is faulty. Thus, in using a syllogism, mistakes can happen in two ways: either from the use of false premises, or from faulty construction of the syllogism. But this use of something false takes place only in one of the premises and not in the other. For, as has been said, through con science the knowledge of synderesis and of higher and lower reason are applied to the examination of a particular act.

However, since the act is particular and the judgment of synderesis is universal, the judgment of synderesis can be applied to the act only if some particular judgment is used as the minor premise. Sometimes, higher reason furnishes this particular judgment; sometimes, lower reason does. Thus, the act of conscience is the result of a kind of particular syllogism. For example, if the judgment of synderesis expresses this statement: "I must not do anything which is forbidden by the law of God," and if the knowledge of higher reason presents this minor premise: "Sexual intercourse will this woman is forbidden by the law of God," the application of conscience will be made by concluding: "I must abstain from this intercourse."

Error has no place in the general judgment of synderesis, as is clear from what we have said earlier, but a mistake can occur in the judgment of higher reason, as happens when one judges something to be licit or illicit which is not, as heretics who believe that oaths are for bidden by God. Therefore, mistakes occur in conscience because of the error which existed in the higher part of reason. Similarly, error can occur in conscience because of error which exists in the lower part of reason, as happens when one is mistaken about civil norms of what is just or unjust, good or bad. Error also occurs because con science does not make a correct application to acts. For, as in constructing speculative syllogisms one can neglect the proper form of argumentation, and thus arrive at a false conclusion, so he can do the same in practical syllogisms, as has been said.

Still, we must remember that in some things conscience can never make a mistake, namely, when the particular act to which conscience is applied has a universal judgment about it in synderesis. For, as in speculative matters, error does not occur when we are dealing will particular conclusions which are derived directly from universal principles and expressed in the same terms—as for instance, no one is deceived in the judgment: "This whole is greater than its part," just as no one is deceived in the judgment: "Every whole is greater than its part" so, too, no conscience can err in the judgments: "I should not love God" or "Some evil should be done." For, in each of these syllogisms, the speculative as well as the practical, the major premise is self-evident in so far as it exists in the universal judgment, and the minor, by means of which the particular predication of identity is made, is also self-evident. This is the case when one says: "Every whole is greater than its part. This whole is a whole. Therefore, it is greater than its part."

Answers to Difficulties:

1. Conscience is called the natural power of judgment in so far as it is a conclusion derived from that power. And in this conclusion there can be error; not, however, because of error in the natural power of judgment, but because of an error of the particular judgment used in the minor premise or because of a faulty reasoning process, as has been said.

2. Conscience adds to scientific knowledge the application of that knowledge to a particular act. There can be error in the application, although there is not error in the scientific knowledge itself. Or we should say that, when I say conscience, I do not imply scientific knowledge (scientia) alone, taken strictly in so far as it deals only will things which are true, but taken in the broad sense for any knowledge (notitia). In this sense, according to the common use of the word, we say that we know (scire) everything will which we are acquainted (novisse).

3. Just as the spark is that part of fire which is purer and hovers above the whole fire, so synderesis is that which is supreme in the judgment of conscience. And it is according to this metaphor that synderesis is called a spark of conscience, nor is it necessary for the relation between synderesis and conscience to be the same as that between a spark and fire in all other respects. Yet, even in material fire the fire receives some modification because a foreign element is added to it, a modification which a spark, because of its purity, does not receive. So, too, some error can find its way into conscience because it has to do will particulars, which are, as it were, matter foreign to reason. This error does not occur in synderesis existing in its purity.

4. Conscience is called the law of understanding by reason of that which it has from synderesis. It is never this, but something else which is the source of error, as has been said.

5. Although reason does not err because it is united to synderesis, still, when higher or lower reason is mistaken, it can be applied to synderesis, just as a false minor premise is united will a true major.

6. The testimony of witnesses is decisive in court when it cannot be shown false through other clear evidence. But, in one whose con science is erroneous, the testimony of his conscience is shown to be false by the very dictate of synderesis. Thus, in the divine court not the testimony of a mistaken conscience, but the dictates of the natural law, will be decisive.

7. Not conscience, but synderesis, is the first rule of human activity. Conscience, however, is a kind of rule which is itself regulated. Hence, it is not strange that it can make mistakes.

8. The hope which is based on a correct conscience has certainty, and this hope is freely given hope. However, the hope which is based on a false conscience is that of which it is said: "The hope of the wicked shah perish" (Pr 10,28).


Parallel readings: Quolibet III, 12, 26; Summa Theol., I, 7 13.


It seems that it does not, for

1. No one is bound to do anything except by some law. But man does not make the law for himself. Therefore, since conscience arises from the act of man, it does not bind.

2. One is not bound to follow the counsels. But conscience operates as a counsel, for conscience seems to precede choice in the way counsel does. Therefore, conscience does not bind.

3. One is bound only by something superior. But the conscience of a man is not superior to the man himself. Therefore, a man is not bound by his conscience.

4. The same thing binds and frees [ an obligation]. But con science cannot free a man [from an obligation]. Therefore, it cannot bind him, either.

To the Contrary:

1'. The Gloss on Ecclesiastes (7:23), "Your conscience knows," says: "No one who is guilty is set free by this judge." But the command of a judge is binding. Therefore, the dictate of conscience binds.

2’. On Romans (14:23), "all that is not of faith...,"Origen says: "The Apostle desires that I say, think, or do nothing against conscience" Therefore, Conscience binds.



Conscience is certainly binding. But, to see how it binds, we must bear in mind that binding, taken metaphorically from corporeal things and applied to spiritual, means imposing necessity. For he who is bound must necessarily stay in the place where he is bound, and the power to go off to other places is taken away from him. Hence, it is clear that binding has no place in things which have internal necessity. For we cannot say that fire is bound to rise, although it is necessary for it to rise. Binding, then, has place only in things which are necessary will a necessity imposed-by something else.

Now, there is a twofold necessity which can be imposed by an out side agent. One is the necessity of coercion, through which someone will absolute necessity does that which the agent forces him to do. Otherwise, it is not properly called coercion, but inducement. The other necessity is conditional, on the presupposition, that is, of an end to be attained. In this way, necessity is so imposed on one that, if he does not do a certain thing, he will not receive his reward.

The first necessity, that of coercion, has no place in movements of the will, but only in physical things, because by its nature the will is free from coercion. The second necessity, however, can be imposed on the will, so that one must, for example, choose this means if he is to acquire this good, or avoid this evil. For, in such matters, avoiding evil is considered equivalent to achieving some good, as is clear from the Philosopher.

Moreover, as necessity of coercion is imposed on physical things by means of some action, so, too, it is by means of some action that conditional necessity is imposed on the will. But the action by which the will is moved is the command of the one ruling or governing. Consequently, the Philosopher says that by means of his command the king is the source of movement.

Similarly, too, where the will is concerned, the relation between the command of a ruler and the imposition of the kind of obligation by which the will can be bound is like the relation between physical action and the binding of physical things through the necessity of coercion. However, the action of a physical agent never imposes necessity on another thing except by the contact of its action will the object on which it is acting. So, no one is bound by the command of a king or lord unless the command reaches him who is commanded; and it reaches him through knowledge of it.

Hence, no one is bound by a precept except through his knowledge of the precept. Therefore, one who is not capable of the knowledge of a precept is not bound by the precept. Nor is one who is ignorant of a precept bound to carry out that precept except in so far as he is required to know it. If, however, he is not required to know it, and does not know it, he is in no way bound by the precept. Thus, as in physical things the physical agent acts only by means of contact, so in spiritual things a precept binds only by means of knowledge. There fore, just as it is the same power by which touch acts and by which the power of the agent acts, since touch acts only by the power of the agent and the power of the agent acts only through the mediation of touch, so it is the same power by which the precept binds and by which knowledge binds, since the knowledge binds only through the power of the precept, and the precept only through the knowledge. Consequently, since conscience is nothing else but the application of knowledge to an act, it is obvious that conscience is said to bind by the power of a divine precept.

Answers to Difficulties:

1. Man does not make the law for himself, but through the act of his knowledge, by which he knows a law made by someone else, he is bound to fulfil the law.

2. Counsel has two meanings. Sometimes, counsel is nothing other than the action of reason inquiring about things to be done. In this sense, the relation of counsel to election is the same as that of a syllogism or question to a conclusion, as is clear from the Philosopher. Taken in this sense, counsel is not opposed to precept, for we take counsel in this way about matters of precept. Hence, obligation can arise from such counsel. It is in this sense that counsel is found in con science in so far as it is applied to one function of conscience, when, namely, it makes an investigation into some action.

In the other sense, counsel is called persuasion or inducement to do something when it does not have compelling force. In this sense, counsel is opposed to precept. Friendly exhortations are of this sort, and, sometimes, conscience proceeds from that type of counsel. For the knowledge of this counsel is sometimes applied to a particular act. But, since conscience does not bind except in virtue of that which is in conscience, conscience which follows from counsel cannot bind in any other way than the counsel itself. Consequently, one is bound not to despise it, but he is not obliged to follow it.

3. Although man is not higher than himself, the one whose precept he knows is higher than man. This is how he is bound by his con science.

4. When a man sins in making the error itself, a false conscience is not enough to excuse him. This is the case when he makes a mistake about things which he is required to know. However, if the error is about things which he is not required to know, be is excused by his conscience, as is clear when one sins from ignorance of a fact, as when one approaches another’s will, whom be thinks is his own.


Parallel readings: Il Sentences, 3; Quolibet III, 12, 27; VIII, 6, x IX,, 15; Ad Rom., c. 14, lectura 2; Ad Gal., c. 5; lectura I; Summa Theol., I-II, 19, 5.


It seems that it does not, form:

1. Augustine says that sin is a word, deed, or desire contrary to the law of God. Therefore, nothing binds under pain of sin except God’s law. But a false conscience is not in accordance will God’s law. There fore, it does not bind under pain of sin.

2. On Romans (1 3: x), "Let every soul be subject to higher powers," Augustine says that we should not obey a lower power contrary to the commandment of a higher power, just as we should not obey the proconsul if his order is contrary to that of the emperor. But a false conscience is inferior to God. Therefore, when conscience gives orders contrary to the commands of God, the command of a mistaken conscience seems to impose no obligation whatever.

3. According to Ambrose, sin is "a transgression of the divine law and disobedience to the heavenly commands." Therefore, whoever disobeys the divine law sins. But a false conscience makes a man disobey the divine power when, for instance, his conscience tells him to do something which is forbidden by the divine law. Therefore, a false conscience leads one into sin if he follows it, rather than binds him under pain of sin if he does not follow it.

4. According to the law, if a man’s conscience tells him that he and his will are related within the forbidden degrees of kindred, and that conscience is probable, then he must follow it against a precept of the Church, even if an excommunication is attached to the precept. How ever, if his conscience is not probable, he is not bound to follow it, but should obey the Church. But a false conscience, especially about things which are intrinsically evil, has no probability at all. Therefore, such a conscience does not bind.

5. God is more merciful than a temporal lord. But a temporal lord does not accuse a man of sin in something which he did by mistake. Therefore, in God’s sight a man is much less obliged under pain of sin by a mistaken conscience.

6. It was said that a false conscience binds will reference to indifferent things, but not will reference to things which are intrinsically evil.—On the contrary, a mistaken conscience is said not to bind when dealing will things which are intrinsically evil because the die tate of natural reason opposes it. But natural reason in like manner opposes the false conscience which is mistaken about indifferent things. Therefore, that, too, does not bind.

7. An indifferent action may be accepted or rejected. But there is no necessary obligation to do or omit an action which may be accepted or rejected. Therefore, conscience imposes no necessary obligation to indifferent actions.

8. If from a false conscience one acts contrary to the law of God, he is not excused from sin. Accordingly, if one who acted against his conscience, even when it was mistaken, were to sin, it would follow that, whether he acted according to his false conscience or not, he would si Therefore, he would be so perplexed that it would be impossible for him to avoid sin. But this seems impossible, because, ac cording to Augustine: "No one sins in that which he cannot avoid." Therefore, it is impossible for such a false conscience to bind.

9. Every sin belongs to some genus of sin. But, if conscience tells one that he should fornicate, to abstain from fornication cannot be classified in any genus of sin. Therefore, he would not sin in thus acting contrary to his conscience. Therefore, such a conscience does not bind.

To the Contrary:

1'. On Romans (14:23), "For all that is not of faith is sin," the Gloss says: "That is, it is a sin in conscience, even if it is good in itself."

But conscience which forbids that which is good in itself is false. Therefore, such a conscience binds.

2’. Observance of the legal prescriptions of the Mosaic law in the new dispensation of grace was not indifferent but intrinsically evil. Hence, Galatians (5:2) says: "If you be circumcised, Christ shall profit you nothing." Nevertheless, conscience prescribing the observance of circumcision was binding. Hence, in the same Epistle (5:3) we read: "And I testify again to every man circumcising himself, that he is a debtor to do the whole law." Therefore, a false conscience binds in things intrinsically evil.

3’. Sin is principally in the will. But whoever decides to transgress a divine commandment has an evil will. Therefore, he sins. Whoever believes that something is a command and decides to violate it wills to break the law. Therefore, he sins. Moreover, one who has a false con science, whether in things intrinsically evil or in anything at all, believes that what is opposed to his conscience is contrary to the law of God. Therefore, if he decides to do that, he decides to act contrary to the law of God, and, so, he sins. Consequently, conscience, no matter how false it is, obliges under pain of sin.

4’. According to Damascene: "Conscience is the law of our under standing."6 But to act contrary to a law is a sin. Therefore, it is also a sin to act against conscience in any way.

5’. One is bound by a precept. But that which conscience dictates becomes a precept. Therefore, Conscience binds, no matter how false it may be.

De veritate EN 150