The paper deals with a letter of emperor Isaakios II Comnenos to the archbishop Iob of Esztergom (ca. 1190), a document which became known through the edition of the letters of the court officer Demetrios Tornikes in 1970. It concerns theological questions (eating of sacrifice meat, filioque) which the emperor (or rather his ghost writer Tornikes) uses to disprove the western practice. In a political explosive time of permanent menace and invasions at all corners of the empire the emperor on the one hand has to underline the orthodox position as the real acceptable in these questions (by sophistically refuting the archbishop’s objections) and to simulate an unshakeable imperial power, on the other hand he wants to give the impression that the archbishop has a special status for the emperor and his patience (which might have consequences for the relation between Byzantium and Hungary, always a needful ally). The paper concentrates especially on the illocution and perlocution aspects of the letter.