Whether blasphemy is always a mortal sin?

❌ Objection 1 : It would seem that blasphemy is not always a mortal sin. Because a gloss on the words, "Now lay you also all away," etc. (Col. 3:8) says: "After prohibiting greater crimes he forbids lesser sins": and yet among the latter he includes blasphemy. Therefore blasphemy is comprised among the lesser, i.e. venial, sins.

❌ Objection 2 : Further, every mortal sin is opposed to one of the precepts of the decalogue. But, seemingly, blasphemy is not contrary to any of them. Therefore blasphemy is not a mortal sin.

❌ Objection 3 : Further, sins committed without deliberation, are not mortal: hence first movements are not mortal sins, because they precede the deliberation of the reason, as was shown above (FS, Question [74], Articles [3],10). Now blasphemy sometimes occurs without deliberation of the reason. Therefore it is not always a mortal sin.