What is conscience according to Saint Thomas Aquinas, and why is it important?


For Aquinas, conscience is the act of applying our general knowledge of good and evil to what we do (or might do). So in order to (naturally) know what is a good action or a bad one, one needs to understand at a general or universal level how things are naturally ordered by God — primarily what human nature is, and what things it needs and deserves. The understanding of this order which dictates what is good or evil behavior is called the Natural Law by Aquinas, and all rational people can and do acquire it simply in virtue of being rational. Some people, however, can so obscure their grasp of the Natural Law through morally bad actions that it becomes as though they forget what is right and what is wrong. God can and does also supernaturally reveal, at the same general or universal level, what is and is not in accordance with his will through His revelation in Scripture, e.g. the Ten Commandments and Christ’s Two Great Commandments.

In addition to a general understanding of right and wrong, one also needs to apply this knowledge to what one does, to the actions one actually performs, and so one needs to be free to act in accordance with what one knows to be the Divine order of things, or not. Our conscience applies the general understanding about what is morally good or bad to what we do. It is our realization that what we might do or have done is good or not, but it is not the actual doing or the choosing. By a further act of the will, called choice, we carry out the act after we, in our conscience, understand that what we are choosing is or is not the morally right thing to do. On a technical note, for Aquinas conscience is the act of understanding which acts are right and wrong, though the name may be applied by extension to a habit or power of performing this act of understanding.  The virtue of making correct judgments about right or wrong, i.e. appropriate exercises of conscience, is called prudence.

The reason that this is important is that one cannot do the right thing if one does not know what the right thing is. So, if someone has problems with their conscience, it does not seem appropriate to blame them. Children do not have fully formed consciences, and do not always understand what is the right thing to do. If a child does wrong because he or she didn’t know any better, or because he or she thought it was the right thing to do (and it wasn’t), we do not (or should not) blame and punish him or her. Aquinas therefore believes that not only is one excused from wrongdoing if one’s conscience is in error, one also is bound to do the wrong thing if one’s conscience tells one that it is the RIGHT thing to do. He also believes that one has a duty to have a well-formed conscience, one that knows what the right thing to do is, and Aquinas is clear that Church authority is a trustworthy guide about what is right and wrong. Even though an erring conscious excuses one from doing wrong, one may have done wrong in letting one’s conscience fall into error.

If you care to read Aquinas on the conscience, you can see Summa Theologiae Ia, q. 79, a. 13 – Whether conscience is a power. Aquinas’ treatment on natural law can be found in ST I-II, q. 92 + ff. I also have an essay in which I try to explain natural law on my web site. (Aquinas on Natural Law.) An overview of ethics, e.g. McInerny’s Ethica Thomistica (Washington, DC: The Catholic University of America Press, 1982) should also prove useful.


What value does our conscience hold when answering questions of faith? As a Catholic can I morally disregard the stated view of the church if my conscience leads me to an opposing viewpoint. You can use a position on birth control as an example.


Is this an assignment? I’ll give a reply anyway, since I think this is an important thing for people to understand. For Aquinas, every conscience binds, even an erring one. This means that if there is something that you believe you cannot do (after having taken care to form your conscience as well as you can), even if the Church commands it, then you cannot do it without committing a sin. Likewise, if there is something you believe you must do, even if the Church forbids it, then you must do it or else commit a sin. (N.B. Aquinas also believes that the Church is an infallible guide in faith and morals, so it could be argued that for one to disagree with the Church, ipso facto, shows one has not formed one’s conscience well.)

So, the command of one’s conscience to do or not do something against what the Church directs has to be pretty strong in order to fit what Aquinas is talking about (if it is even practically possible). I doubt if many people disobey the Church’s prohibition on artificial contraception because they have sought to develop a well-formed conscience and this conscience is telling them that they must take the pill. Though an erring conscience binds, an erring conscience does not simply mean one does not have to obey any authority; it is not a license to “disregard” anything. Conscience is an authority, and, in the end, it is what one has to obey. If one is convinced that Church is just wrong (and they made honest, good faith efforts to know and accept what the Church teaches), I would say they suffer from an erring conscience, and that would bind them in their actions.

Of course, such a person would not and could not know they are in error. That is, it is not possible for a person to believe that she herself has an erring conscience. It is the nature of a conscience (both erring and true) to believe that it is true. But believing that one is right does not ipso facto, make one right. That just is what it means to have an erring conscience: believing one is right when one is not, in fact, correct. So, if one’s conscience is in error, one would, by that very fact, be blind to the error.

To say that one is bound to follow an erring conscience is not to say that one is morally justified in doing any- and everything one is inclined to do. If every action was morally right just because one wanted to do it, it would be logically impossible to commit any morally wrong act; and this would empty “morally right and wrong” of any meaning. Moreover, everyone knows that certain actions by individuals just are morally wrong, and the individuals who did them are guilty of wrongdoing, despite the fact that the perpetrator thought it was a good thing. One does not need to appeal to exotic and notorious cases of Nazis or slave owners to see this, but it is apparent in everyday cases like that of Matthew Shepard. In such cases, even an “erring conscience” does not justify or excuse the moral evil.

But short of having the subjective conviction (after exercising due diligence to form one’s conscience well) that one has to act contrary to Church authority, or that one may not morally obey Church authority, that is, if one is not sure one is right, one has (Aquinas would say) an erring opinion (not an erring conscience)(See ST II-II, q.5, a.3 cited above), and in that case, one is morally bound not to act contrary to a trustworthy authority (e.g., the Church). Such a person would have a doubtful conscience, and one morally cannot act with such doubts, any more than a hunter may shoot at a rustling bush if it might be hiding another hunter and not a deer (assuming deer hunting is morally licit per se).

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