A Sin is a Sin – 28 January 2023

Gessi St. Thomas A Sin is a Sin
The Temptation of St. Thomas by Francesco Gessi, 1632-1633. St. Thomas says “no” to sin

What is Truth? 

    “What is truth?” –  I seem to remember someone raising the question somewhere.  For the ideologue, “truth” is whatever promotes the ideology, and if it happens to correspond with reality that’s fine. If it doesn’t, no problem, we’ll make something up. Followers of  Him who is “The Way, The Truth, and The Life” (John 14:6) know better . . . or we should know better. Truth isn’t something we create to serve our own purposes, it exists beyond and above us.  We can’t manufacture truth, but we can discover it.

     One of the Church’s greatest discoverers and teachers of the truth is St. Thomas Aquinas, Doctor of the Church. We celebrate his feast day today. Idealogues in the Church will often use his name, when it suits their purposes, to promote their heterodox version of Catholicism. As we shall see, however, it isn’t easy to exploit St. Thomas.

Below is a revised version of the very first blog post I published, nine years ago.  Since “Truth” is a perennial theme (see here, here, and here), this seems a good day to republish “A Sin is a Sin: St. Thomas and Conscience.”

When is it A Sin Not To Sin? 

   St. Thomas Aquinas, greatest of Catholic theologians, is the target of a sort of “hostile takeover.” That is to say, I’ve heard some people invoke his authority in order to justify ignoring Catholic moral doctrine. They point out that St. Thomas says it’s wrong not to follow our conscience, even if it’s in error.  Therefore (they say), if our conscience tells us to use contraceptives, or support pro- abortion politicians, or vote in favor of redefining marriage, we would actually be sinning if we obeyed the Church!  Don’t blame them, these people add. St. Thomas Aquinas made them do it.  What else can they do?

     What can any of us do? Well . . . we can let the Angelic Doctor speak for himself. On the one hand, St. Thomas does actually say what the dissenters claim he says, that we are morally bound to follow our conscience. On the other hand, if we look at all of what he says, he actually means the opposite of what they say he means.  Let’s look at the relevant passage from his Summa Theologiae  [ST hereafter]:

. . .  conscience is nothing else than the application of knowledge to some action. Now knowledge is in the reason. Therefore when the will is at variance with erring reason, it is against conscience. But every such will is evil; for it is written (Romans 14:23): “All that is not of faith”–i.e. all that is against conscience–“is sin.”

Therefore the will is evil when it is at variance with erring reason.  ST IiaIae


Conscience is not Feelings or Opinions 

St. Thomas composing - A Sin is a Sin
St. Thomas composing the Summa (image from aquinasonline.com)

Yes, it is “evil” to disobey even an erroneous conscience. But here’s the key. Conscience does not mean “feelings” or “opinions” (the common misrepresentation). Rather, conscience is “the application of knowledge to some action.”  To St. Thomas (and to the Church) it is the process of applying moral principles to one’s particular situation. In another section he describes it as “knowledge applied to an individual case.” (ST I, 79, 13).

Since conscience is the reasoning process by which we determine whether a course of action is good or evil, going against conscience means deliberately choosing what we believe to be evil, even if we do not actually accomplish evil:

But when erring reason proposes something as being commanded by God, then to scorn the dictate of reason is to scorn the commandment of God.  (ST IiaIae)

When we violate our conscience, then, quite apart from the actual harm we might or might not be doing (objective sin), we are intentionally rejecting what we believe to be God’s will (subjective sin). The “evil” in violating our conscience is our conscious choice to disobey God. This act of defiance is a sin in itself, quite apart from the sinfulness (or not) of the particular act we are contemplating.


Forming Our Conscience 

The story doesn’t end there, of course. St. Thomas was well aware that someone might try to use his argument to justify sin. He goes on to explain that, even though we must obey an erroneous conscience, we might be morally culpable (i.e., guilty of sin) for having an erroneous conscience.  He says:

If then reason or conscience err with an error that is voluntary, either directly, or through negligence, so that one errs about what one ought to know; then such an error of reason or conscience does not excuse the will, that abides by that erring reason or conscience, from being evil. But if the error arise from ignorance of some circumstance, and without any negligence, so that it cause the act to be involuntary, then that error of reason or conscience excuses the will, that abides by that erring reason, from being evil.  (ST IiaIae)

What One Ought to Know 

St. Thomas did not make her do it

Recall that conscience is moral principles (what he calls “knowledge” or “Divine Law”) when we apply it to particular circumstances.   We don’t get to create those moral principles for ourselves. For an adult Christian “what one ought to know” are the moral principles contained in Church teaching. Now,it is quite possible to be mistaken or misinformed, through no fault of one’s own (invincible ignorance), about the circumstances to which one is applying the principles. Therefore, invincible ignorance excuses us from subjective guilt. Failure to form our conscience properly does not.

   Just to be sure his point is clear, St. Thomas illustrates with the following examples:

For instance, if erring reason tell a man that he should go to another man’s wife, the will that abides by that erring reason is evil; since this error arises from ignorance of the Divine Law, which he is bound to know. But if a man’s reason, errs in mistaking another for his wife, and if he wish to give her her right [i.e., sexual intercourse] when she asks for it, his will is excused from being evil: because this error arises from ignorance of a circumstance, which ignorance excuses, and causes the act to be involuntary. (ST IiaIae)

Notice the phrase “bound to know.”  Whether or not adultery is wrong is not a matter of conscience. Its wrongness is an unalterable reality that we are “bound” to acknowledge.


The Wages of Sin 

       When the champions of conscience (or perhaps more properly, “conscience”) over and against Catholic moral doctrine invoke St. Thomas, it is almost always in order to justify their rejection of the Church’s teaching on one of the currently fashionable sexual issues, such as contraception, gay marriage, extra-marital sex, and so on. Scripture and the teaching of the Church have unambiguously condemned these practices under the sixth commandment’s prohibition of adultery.

If we look at St. Thomas’s entire discussion, however, and not just the one sentence that seems to excuse dissent, we see that he is saying explicitly that you cannot invoke conscience against these teachings. He uses adultery as his example to demonstrate that the role of conscience is not to determine basic rules of right and wrong. Rather, it is to guide our own actions according to the sure rules we have received from God through his Church.


Three Strikes You’re Out 

     It would be helpful at this point to recall that sin involves a lot more than just the will of the sinner. The Church teaches that there must be three conditions for a sin to be a mortal sin: grave matter, full knowledge, and full consent. In other words, “it’s bad, you know darn well it’s bad, but you go ahead and do it anyway.”

St. Thomas is here considering only the second part of the formulation, that is, whether or not you know darn well it’s bad.   Even if, through no fault of your own (a significant “if”, as we saw above) you don’t know it’s bad, and so are not guilty of choosing bad, it’s still bad.  And it’s bad because bad consequences, for you and/or society at large, are likely to follow.


 All Manner of Destructive Consequences 

    That’s why it’s a sin, after all. Consider St. Thomas’s example of the unwitting adulterer.  He is not guilty of subjective sin, because he is not aware of what he is doing.

The act is nevertheless an objective sin, which could lead to all manner of destructive consequences. Fathering a child out of wedlock (with all the attendant problems) is one. So is contracting a disease which might in turn infect his innocent wife. Let’s not forget the other woman. She might receive an infection from him, and, depending on her awareness of the situation, might feel exploited or betrayed by him.  If the adultery becomes known, as is likely, it will damage the man’s relationship with his wife and children. If not, he may feel the need to cover up his deed and commit the further sin of lying in order protect his family . . .  And on and on.

A Sin is a Sin

   In other words, a sin is a sin is a sin, and whatever we may think, it’s still a sin.  As Catholics, we have ample means of knowing the Moral Law, and therefore have no excuse for disobeying it.  We have it straight from the Ox’s mouth. Nothing justifies committing acts which the Church teaches to be morally wrong.



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