Now all the foregoing are done seriously and not in jest. Therefore derision differs from all of them. And since this end is distinct from the others, it follows that the sin of derision is distinct from the foregoing sins. It is accordingly evident that derision agrees with the foregoing vices as to the matter but differs as to the end. A secure and calm conscience is a great good, according to Prov.
Every mortal sin is contrary to charity.
Therefore derision cannot be a mortal sin. Further, the greatest derision would appear to be that which is done as an injury to God. Therefore derision is not a mortal sin. Further, reviling and backbiting seem to be graver sins than derision, because it is more to do a thing seriously than in jest. But not all backbiting or reviling is a mortal sin.