Fornication of the heart


Is there such a sin as fornication of the heart? And is it a mortal sin?The reason I ask is because of matthew 5: 27-30,which pertains to adultery but foes it pertain to fornication. The catechesim says that fornication is a carnal union so I am confused. CCC 2353 Fornication is carnal union between an unmarried man and an unmarried woman. It is gravely contrary to the dignity of persons and of human sexuality which is naturally ordered to the good of spouses and the generation and education of children. Moreover, it is a grave scandal when there is corruption of the young.


You will note that CCC 2353 discussing fornication is in the section of the catechism that discussed the sixth commandment in general. Fornication is included as a sin against the sixth commandment and is considered grave.

Have your read that section in entirety? I think it will answer your questions:

You will note that Mt 5:27-28 is quoted at the very top to indicate that it refers to everything discussed below. The section covers sins against chastity and marriage, whether they are the narrow/strict definition of adultery or the more broad meaning understood by the commandment.


Thank you,


I don’t remember chapter and verse but when Jesus was asked about divorce, I think, He said that anybody who thinks lustly about another has already committed adultery in his heart. Maybe somebody else can flesh this out with chapter and verse.:shrug:


Yes -while that is not a normal “term” for lust - yes that is mortal sin.

Jesus yes used the term “adultery” there…but such lusting even involving unmarried persons is still the mortal sin of lust…


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