Indeed. This penchant here at CAF of continuously parsing sin to be either “venial” or “mortal” confounds me. Many have a tendency to say “oh, that’s just venial” and leave it at that. Sin is sin and should all be rightly avoided. I place much of the blame on the catechism because now everyone thinks that it makes them a junior theologian.
The first and most important point is that any person suffering from scrupulosity discusses their doubts with a single good priest, and follows his advice absolutely. Scrupulous people should absolutely follow the 10 commandments for the scrupulous, as much as they should follow the 10 commandments of God.* St Alphonsus Liguori said that the information about venial sin becoming mortal sin should always be discussed with the confessor, when you are scrupulous*
10 commandments for the scrupulous: fisheaters.com/scruples.html
(No support for the site intended. Only this link is good, but it is not too faithful to the Pope)
If one knows as a fact that the sin they’re committing is venial matter, then it’s a venial sin, even if the sin is objectively grave matter. Ex: I was certain that fully consenting to unchaste thoughts was venial matter, even though it is objectively grave matter.
If one isn’t sure if the sin they are committing is venial or grave matter, then the sin is always grave, even if it was actually venial matter. Ex: I wasn’t sure if overeating is venial or grave matter, but overeat anyway. It would be grave matter, since I was willing to choose grave sin without clearing that doubt.
If I commit a venial matter, thinking that it is actually grave matter, then my intentions cause me to commit grave matter. Ex: I think that overeating a little is grave matter, even though it’s objectively venial matter. If I still overeat thinking that I’m committing mortal sin, then I commit mortal sin.
SIDE NOTE: Only for scrupulous people, if you are unsure if something you will do is a sin at all, or no sin, then it’s no sin. The confessor we go to can tell us if we are scrupulous or not.
While I agree with the comments above that we should avoid all sin, even venial, still I think the distinction between mortal and venial is useful for the layman. It is important to know whether or not one is in a state of grace.
The person said nothing of the sort but simply asked the question.
Leave the persons reasons for asking the question to them - and to their confessor.
We all struggle with venial sins - and yes that might be a deliberate venial sin - but yet one of great habit or weakness etc (knowingly eating too much icecream or too much turkey at Thanksgiving…) Not of malice.
Yes one should work on such and avoid such - but lets keep to the question asked.
A nice summary regarding mortal sin and venial sin from the Compendium issued by Pope Benedict XVI
395. When does one commit a mortal sin?
One commits a mortal sin when there are simultaneously present: grave matter, full knowledge, and deliberate consent. This sin destroys charity in us, deprives us of sanctifying grace, and, if unrepented, leads us to the eternal death of hell. It can be forgiven in the ordinary way by means of the sacraments of Baptism and of Penance or Reconciliation.
396. When does one commit a venial sin?
One commits a venial sin, which is essentially different from a mortal sin, when the matter involved is less serious or, even if it is grave, when full knowledge or complete consent are absent. Venial sin does not break the covenant with God but it weakens charity and manifests a disordered affection for created goods. It impedes the progress of a soul in the exercise of the virtues and in the practice of moral good. It merits temporal punishment which purifies.
1862 One commits venial sin when, in a less serious matter, he does not observe the standard prescribed by the moral law, or when he disobeys the moral law in a grave matter, but without full knowledge or without complete consent.
1863 Venial sin weakens charity; it manifests a disordered affection for created goods; it impedes the soul’s progress in the exercise of the virtues and the practice of the moral good; it merits temporal punishment. Deliberate and unrepented venial sin disposes us little by little to commit mortal sin. However venial sin does not break the covenant with God. With God’s grace it is humanly reparable. “Venial sin does not deprive the sinner of sanctifying grace, friendship with God, charity, and consequently eternal happiness.”
The deliberate turning one self away from God by thumbing one’s nose at his very reasonable way of life, would be a mortal sin. An action in and of itself would not be a mortal sin. But testing and defying God’s Mercy would be a grave mistake.
There is a difference between being scrupulous and being defiant and rude to God in His love for us.
+The highlights above indicate that there is grave danger in constant turning away from **God ** . . . and deliberately rebelling and indulging in venial sin time and time again . . . . choosing self above God . . . for it disposes the soul to becoming colder and colder in rejecting our Wonderful Lord and the goodness of the healthy **Holy Pathways of God **which are there for our good as God’s children . . .
Deliberately choosing evil . . . *over and over again *. . . callouses the soul and . . . hardens . . . the heart . . . and creates greater and greater distance of the soul from its . . . **Blessed and Needed LORD and Saviour **. . . and its need for salvation, conversion and growth in holiness . . . and sickens and deceives the mind of mankind to the point where the soul becomes no longer particularly interested in God and His healthy and Holy Ways created for their good . . . and in due season the cold and callous soul who indulges themselves in known venial sin is likely to naturally indulge in mortal sin when the temptation comes along . . . with little to no concern whatsoever about wounding the tender loving Heart of our dear Blessed LORD their Saviour . . .
We need to be . . . very very careful . . . not . . . to forget the serious prophetic warnings our LORD gave to the seven churches in Sacred :bible1: Scripture in Revelation . . . three of which are quoted below . . .
Ignoring . . . **God and His Holy Pathways of Good **. . . for our souls is . . . **never **. . . a good idea . . . never . . . ever . . . and is utter self-deception . . . to the destruction of our souls . . .
[INDENT][INDENT]THE CHURCH AT EPHESUS
:bible1: Revelation 2:1a, 4-5
 Unto the angel of the church of **Ephesus **write: …  But I have somewhat against thee, because thou hast left thy first charity.  Be mindful therefore from whence thou art fallen: and do penance, and do the first works. Or else I come to thee, and will move thy candlestick out of its place, except thou do penance.
THE CHURCH AT SARDIS
:bible1: Revelation 3:1
 And to the angel of the church of Sardis, write: These things saith he, that hath the seven spirits of God, and the seven stars: I**** know thy works, that thou hast the name of being alive: and thou art dead.
THE CHURCH AT LAODICEA
:bible1: Revelation 2:14-17
 And to the angel of the church of Laodicea, write: These things saith the Amen, the faithful and true witness, who is the beginning of the creation of God:  I know thy works, that thou art neither cold, nor hot. I would thou wert cold, or hot.  But because thou art lukewarm, and neither cold, not hot, I will begin to vomit thee out of my mouth.  Because thou sayest: I am rich, and made wealthy, and have need of nothing: and knowest not, that thou art wretched, and miserable, and poor, and blind, and naked.
[RIGHT]. . . all for Jesus+
. . . thank You Blessed Sweet Spirit of our Holy God+
. . . thank you Blessed Holy Mother Church+
. . . thank you Blessed St. Jerome+[/RIGHT]