Whether simple fornication is a mortal sin?

❌ Objection 1 : It would seem that simple fornication is not a mortal sin. For things that come under the same head would seem to be on a par with one another. Now fornication comes under the same head as things that are not mortal sins: for it is written (Acts 15:29): "That you abstain from things sacrificed to idols, and from blood, and from things strangled, and from fornication." But there is not mortal sin in these observances, according to 1 Tim. 4:4, "Nothing is rejected that is received with thanksgiving." Therefore fornication is not a mortal sin.

❌ Objection 2 : Further, no mortal sin is the matter of a Divine precept. But the Lord commanded (Osee 1:2): "Go take thee a wife of fornications, and have of her children of fornications." Therefore fornication is not a mortal sin.

❌ Objection 3 : Further, no mortal sin is mentioned in Holy Writ without disapprobation. Yet simple fornication is mentioned without disapprobation by Holy Writ in connection with the patriarchs. Thus we read (Gn. 16:4) that Abraham went in to his handmaid Agar; and further on (Gn. 30:5,9) that Jacob went in to Bala and Zelpha the handmaids of his wives; and again (Gn. 38:18) that Juda was with Thamar whom he thought to be a harlot. Therefore simple fornication is not a mortal sin.

❌ Objection 4 : Further, every mortal sin is contrary to charity. But simple fornication is not contrary to charity, neither as regards the love of God, since it is not a sin directly against. God, nor as regards the love of our neighbor, since thereby no one is injured. Therefore simple fornication is not a mortal sin.

❌ Objection 5 : Further, every mortal sin leads to eternal perdition. But simple fornication has not this result: because a gloss of Ambrose [*The quotation is from the Gloss of Peter Lombard, who refers it to St. Ambrose: whereas it is from Hilary the deacon] on 1 Tim. 4:8, "Godliness is profitable to all things," says: "The whole of Christian teaching is summed up in mercy and godliness: if a man conforms to this, even though he gives way to the inconstancy of the flesh, doubtless he will be punished, but he will not perish." Therefore simple fornication is not a mortal sin.

❌ Objection 6 : Further, Augustine says (De Bono Conjug. xvi) that "what food is to the well-being of the body, such is sexual intercourse to the welfare of the human race." But inordinate use of food is not always a mortal sin. Therefore neither is all inordinate sexual intercourse; and this would seem to apply especially to simple fornication, which is the least grievous of the aforesaid species.