Whether flattery is a mortal sin?

❌ Objection 1 : It seems that flattery is a mortal sin. For, according to Augustine (Enchiridion xii), "a thing is evil because it is harmful." But flattery is most harmful, according to Ps. 9:24, "For the sinner is praised in the desires of his soul, and the unjust man is blessed. The sinner hath provoked the Lord." Wherefore Jerome says (Ep. ad Celant): "Nothing so easily corrupts the human mind as flattery": and a gloss on Ps. 69:4, "Let them be presently turned away blushing for shame that say to me: 'Tis well, 'Tis well," says: "The tongue of the flatterer harms more than the sword of the persecutor." Therefore flattery is a most grievous sin.

❌ Objection 2 : Further, whoever does harm by words, harms himself no less than others: wherefore it is written (Ps. 36:15): "Let their sword enter into their own hearts." Now he that flatters another induces him to sin mortally: hence a gloss on Ps. 140:5, "Let not the oil of the sinner fatten my head," says: "The false praise of the flatterer softens the mind by depriving it of the rigidity of truth and renders it susceptive of vice." Much more, therefore, does the flatterer sin in himself.

❌ Objection 3 : Further, it is written in the Decretals (D. XLVI, Cap. 3): "The cleric who shall be found to spend his time in flattery and treachery shall be degraded from his office." Now such a punishment as this is not inflicted save for mortal sin. Therefore flattery is a mortal sin.