According to Catholicism, a venial sin is a sin which meets at least one of the following critera:

1. it does not concern a "grave matter",
2. it is not committed with full knowledge, or
3. it is not committed with both deliberate and complete consent.

Such a sin involves a "temporary loss of grace" from God.

As the above critera are the three criteria for mortal sin stated negatively (via de Morgan's theorem), a sin which met none of these extenuating conditions would necessarily be considered mortal.

Each venial sin that one commits adds to one's time in purgatory. A venial sin can be left unconfessed. Venial sins remain venial no matter how many one commits; they cannot "add up" to collectively constitute a mortal sin.

See Jeremiah 7:26, Lamentations 4:6, Ezekiel 16:44-58, 1 John 5:16-17, Matthew 11:22, John 19:11, 1 John 5:16-17.

"The Venial Sin" is a short story by Honoré de Balzac.