Why is immoral sex always a grave matter?

I am confused on what Mortal Sin means and why some things are considered mortal sins while others are not. Now before I go any further, I want to be clear that I am not looking for any loopholes or work-around; I am ONLY looking for some form of consistency. That’s all I want: consistency.

I read the catechism, but it didn’t help.


Basically, I would like a rule of thumb for what makes something grave matter? Why is it that, while all other violations of the ten commandment fall under a spectrum with lots of room between mortal and non-mortal.

Here’s what I mean illustrated by some examples:

Deceit is a sin, lying to a courtroom to get someone wrongly convicted of a capitol offense is a mortal sin, and lying about your favorite sports team to avoid an argument is only a venial sin.

Meanwhile lust is a sin, cheating on your spouse with a prostitute while away on a business trip is a mortal sin, but so is having sex with your spouse in a non-procreative way.

This feels problematic for two reasons.

The first, as previously mentioned, is that there is no scale. An unrepentant masturbater and an unrepentant serial rapist get the same punishment when they die, despite one being many magnitudes worse than the other.

The second problem is that the rule of thumb I usually use to gauge gravity can’t be applied. For other sins it is easy to point out who is being hurt and how badly he/she is being hurt. Murder is a mortal sin because the victim is deprived of life, grand theft is a mortal sin because the victim is deprived of resources that might be irrecoverable, but who is being hurt in masturbation and in non-procreative marital intercourse? When explaining why these are grave matters nobody ever points to anyone being hurt, instead they say “it is intrinsically evil because God forbade it because it is intrinsically evil because …”.

So can anyone explain how I am misunderstanding the catechism and/or why it isn’t inconsistent for ALL non-natural sex to be grave matters when not all acts of violence and/or theft share that distinction?

There is s scale. Looking at a woman lustfully could be venial. Could also become mortal depending on how one entertains the thoughts.


Did you read this part from the catechism?

1857 For a sin to be mortal, three conditions must together be met: "Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent."131

Motive is what makes immoral sex a grave matter. Most of us want what we want when we want it. If love of the person isn’t the motive, then the sexual sin can well be grave or approaching grave matter with knowledge and consent mitigating factors. If you love a person you won’t want to lead them into sin. You will want to help them reach eternal salvation.

Hope this helps.

It is difficult to have immoral sex accidentally, unless you are already engaged in mortally sinful activities or pushing the limits of sensible behavior.

Of course, there can be extenuating circumstances. But if you are ever in a situation where immoral sex is so casual that it seems like a venial sin, and it is not a situation of a badly educated married couple, you are in a very bad place with very bad company, and probably committing all different kinds of mortal sin.

As for “who is being hurt,” obviously all sexual mortal sin is self-destructive sexual behavior. People hurt their capacity to love and their own psychological well-being. They twist their minds and misuse or abuse their bodies, and they do the same to any immoral sexual partner.

But the measure of sin is offending God. A baptized Christian is a temple of God, and sin is desecration of our perpetual worship of Him, an attempt to kick Him out or drag Him along as a spectator, while disobeying Him and denying the purposes for which we were created.

One reason that sexual sins constitute grave matter is that sex is the means by which married people (in ordinary circumstances) become co-creators with God. The fact that new life - new men and women made in God’s image - is the fruit of our human sexuality makes it a big deal.

Obviously some sins are worse than others, even within the mortal/venial distinction. That’s one reason we have penance. But yes, unrepentant serious sin is a very dangerous position to be in regardless of the particular sin. All that’s required is contrition, though, and God will show mercy.

The problem is in the way you are looking at sin. Your looking at the sin itself. That’s not the right approach to understand judgement from God. The main thing you want to look at is intention, the why of the sin. Conversely, in order to understand the obligation or in some cases guidance, you must also understand the why, and not just think of obligations as being arbitrary.

There are sins that are worse than others, hence mortal and venial sins. But there is no reason to take things farther than that because intention (which is the term I’m using to describe the combination of knowledge and culpability) is where the heart of the matter is. Intention is only rightly judged by God. We can call a sin a sin but we cannot impart the judgement of mortal or venial sin, but only offer our opinions when asked by only the sinner, because we cannot know a persons heart like God does.

I’ve heard it said that every sin can be put somewhere in the context of the ten commandments, and therefore every sin is grave matter. This is obviously not the case. So you see the problems that arise when theologians discuss sin. And you see why the CCC is written the way it is.

God bless you in your journey.

A bit of a tangent, but to clear up a seeming misperception in the first post, the Church does not teach that everyone in mortal sin is given the same punishment. In fact, it has taught that punishment will be worse for worse sinners. Everyone in Hell is denied the beatific vision of God, but from there it varies.


Grave matter is grave matter. Motive does not necessarily determine gravity.
Motive conditions culpability in mortal sin.

To answer the OP’s question…morality is the evaluation of human acts in reference to “the good”.
Your question about determining gravity necessitates knowing what the good in question is. Without knowing what the good is, we are merely left wondering why something is prohibited.

What are the goods that sexuality points to?
You have the existence and flourishing of human life as a good. The unity of spouses. The dignity of the human person.

Because these things are so good, offenses against them tend to be grave matter. And the gravity of disordered action remains whether or not all the conditions for mortal culpability apply.

Check out the part I bolded. Who says? They both go to hell but one is tormented more than the other.

Says who? Not your call.

Only if there was lack of knowledge or consent!

Looking lustfully is a mortal sin (grave matter for mortal sin).

a… no.

The hell of the one latter will be much worse than the hell of the former.

Again the nature of the lies are different - the nature of the matter.

To lie to do grave harm to another is a grave sin. To lie under oath in a court likewise -for it regards a serious oath (breaking of it).

A venial lie about some team is a very different matter in itself.

Yes both are gravely opposed ones marriage. Both are sins against chastity etc. Grave sins.

While 2 things can both be mortal sins it is also true that one mortal sin can be worse than another mortal sin…bring with it worse effects etc.

(yes sex of the unmarried - outside of marriage does hurt the persons involved in various ways (selfishness, lying etc etc)-but that that is not the main reason it is seriously wrong).

The gravity of a matter is not simply about who it may hurt - or the consequences - but also due to the very nature of what it goes against (yes sex outside of marriage does hurt the persons involved in various ways -but that that is not the main reason it is seriously wrong).

Tis the very nature of the serious and sacred nature of sex and marriage.

Questions of morality only gain their full meaning in light of the good at hand.

All sin is first an offense against God. Sin is the misuse of His creature. God not only loves us into existence, He sustains us. And when we sin, we require our loving Creator to sustain us even in our evil act.

Man’s sexual faculty calls upon God in a unique and special manner to participate in the creation of new life. If we misuse our sexual faculty, we call upon Holiness Itself to participate in our evil act. What could be graver than causing God to be proximate to our evil?

Ah, okay. This explanation makes sense; if God is involved in every sex act, then misusing it would be the equivalent of defecating on a bible.

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