How to Identify Mortal Sin

Catholics know that in order for a sin to be mortal, to kill the divine life of grace in one’s soul, three conditions need to be met.  It must be grave matter, done “with full knowledge and deliberate consent” (CCC 1857).  The issue is that nobody seems to know what full knowledge or deliberate consent precisely mean.  Nobody seems to be able to distinguish venial from mortal sin. 

            Grave matter refers to what is done, to the action.  The act has to be grave, serious, very harmful to oneself or others.  This is a much easier distinction.  People can think about it in terms of the difference between a felony crime and a misdemeanor.  Felonies are serious acts that seriously hurt people while misdemeanors are certainly bad, but not seriously so.  Traditionally, Catholics would identify direct violations of the ten commandments as sins of grave matter. 

            The next two conditions for mortal sin, full knowledge and consent, refer to the rational aspects of the act.  An act only has moral weight or value when it is a rational and human act, an act done with intellect and will.  If one or both of these faculties is absent, then theologians call the act an act-of-man instead of a human act which is morally relevant.  The second condition – full knowledge – refers to the intellect and the third condition – deliberate consent – refers to the will.  Simply put, one has to know that the act is wrong and still choose to do it. 

            The second condition, full knowledge, does not simply mean that one knows that the act is wrong.  One has to know that the act is an act of grave matter – you have to know it is gravely wrong.  If one is ignorant of the evil of the act, or ignorant of its gravity, then the act is less rationally chosen (you did not intend or choose to do a gravely evil thing) and thus less morally blameworthy (manslaughter is not as bad as premeditated murder).  Yet not all ignorance excuses one. 

            There are three conditions or criteria that must be met in order for ignorance to excuse one’s act.  First, one has to be ignorant about the evil or the gravity of the evil – you have to truly not know the act is (gravely) wrong, pretending to be ignorant does nothing but make you a liar.  Second, you cannot be at fault (morally culpable) for not knowing the act is (gravely) evil.  If this is something you should and could reasonably have known then your ignorance does not excuse.  Otherwise said, if you don’t know because you were lazy and failed to seek the truth, if your ignorance is a result of a sin of omission, then your ignorance does not excuse you.  Third, if you had known the moral gravity of the act, you would not have committed it.  Ignorance will not excuse you if you would have done it regardless because your will is still evil. 

            At this point people often wonder what falls under the second criteria, what people ought to know about the moral law.  Should and can we know all grave or intrinsic evils?  Are we responsible for our moral formation?  Typically, the response is that we must take people’s conditions and opportunities for learning into account.  For example, the average secular high schooler in America has probably never heard that pornography is immoral.  Instead, they have heard their entire lives from all authorities that it is a good and normal expression of one’s sexuality, they are even told it is unhealthy not to use it.  How could we expect these people to know pornography is immoral when all their teachers, coaches, friends, and even doctors recommend it and, if they even go to Church, they probably have never heard a sermon against it?  So, many high schoolers in America probably have ignorance for which they are not culpable about the use of pornography. 

            Also, it is clear from scripture that good people can be ignorant, through no fault of their own, about grave evils.  In Genesis 22, God commands Abraham to sacrifice his only son Issac.  We know that human sacrifice is a grave evil that God detests.  Abraham does not question God but proceeds to prepare for the sacrifice.  In Abraham’s culture human sacrifice was a normal and acceptably form of worship.  Abraham saw nothing intrinsically evil about it, certainly it was an incredibly hard command to follow and he had to demonstrate great faith in God, but he did not see it as a command to sin.  If he had, he would not have followed it for he knew God was good and only commanded good things.  Of course, God did not actually want Abraham to kill Issac and thus stopped him, teaching him that human sacrifice is evil.  But this highlights just how gravely ignorant well-meaning people can be. 

            The third condition for mortal sin – deliberate consent – refers to the act of the will.  One has to choose the evil act oneself.  Typically, acts we choose are free.  But several factors can diminish our capacity to choose freely.  These are called the enemies of the voluntary.  There is coercion.  If one is coerced by physical force, social pressure, or some leader to do an act, one is less free in it and thus less culpable for such acts.  Everyone knows that what people do under duress is not really their own free choice.  Next there is passion or emotion.  When we are experiencing some strong emotion, desire, or passion to do some act we become less free to rationally choose what to do.  Many people find themselves doing acts due to passion that they would otherwise never do, acts they know are wrong and hate.  Even St. Paul says, “I do not understand my own actions.  For I do not do what I want, but I do the very thing I hate” (Romans 7:15).  Such passions reduce, but do not totally destroy, our freedom. 

            These things, coercion and passion, hurt our ability to make a free choice.  But after we have committed a sin, how do we know if we were sufficiently free or not?  There are signs that we can study, chiefly the consequent passions.  The consequent passions refer to the emotions or feelings we experience after (hence consequent) an act.  They are simply how we feel about what we did immediately after doing it.  There are two main consequent passions: pleasure and sorrow.  Pleasure after an act shows that one’s will fully consented to the act and now, having done the act, one’s will reacts with pleasure.  On the other hand, sorrow after an act shows that one did not fully consent to the act and hence one’s will rejects what one did.  A stronger pleasure indicates a stronger consent (or lack of consent with sorrow).  The quicker the consequent pleasure arises (immediately or after a few minutes or a few hours or a few days) is also a sign of stronger consent (or lack thereof with sorrow).  So, if one commits a sin and immediately feels guilty and bad about what one did, and feels this strongly, that is a sign that one’s consent to the act was weak and probably some enemy of the voluntary was present – likely you only did it through fear or some strong desire in the moment – not a mortal sin.  But, if one feels pleasure in one’s sin, if one is pleased with oneself for doing it, that is a sign of strong consent to the sin. 

            So, we can know what constitutes full knowledge and deliberate consent for mortal sin.  One key thing to note.  Even if one is lacking in knowledge or freedom to consent and thus the sin is only venial, any sin of grave matter is going to be very harmful to oneself and to others.  Even if there are excusing factors, genuine ignorance or lack of consent, the nature of a gravely evil act still occurs, and such acts are very dangerous.  The average American secular high schooler who has ignorance about pornography is still habituating himself to be selfish and abusive and will hardly be able to form an authentic friendship, not to mention the radical addiction likely to occur.  Manslaughter still kills a person and devastates their family.  Thus, we must seriously wage war against any sin of grave matter (and venial sins!), not just mortal sins.