Abstract
Knowledge of sins of speech derives from knowledge of God and from knowledge of created nature as teleological, rational, social and communicative. Speech is directed to God and neighbours; it is causal and irrevocable; good speech demonstrates integrity, good intent, justice and moderation. Sinful speech arises from wicked intention and damages both speaker and hearer. Blasphemy opposes vocal confession of God with disparagement of his excellence. Defamation opposes justice by speaking against the neighbour’s good reputation. In the Christian community, the speech of regenerate creatures is under repair, as thanksgiving to God and edification of neighbours are established by the moving power of the Holy Spirit.