Introduction. At the end of the sixth century a dispute broke out between the popes and the patriarchs of Constantinople – first of all, between pope Gregory I the Great (590–604) and patriarch John IV the Faster (582–595) – over the epithet “Ecumenical”, which appeared in the title of John of Constantinople. This dispute is quite widely represented in the scientific literature, but since researchers almost always pay attention to this topic in general, their papers often miss many nuances contained in the texts of the letters of pope Gregory. Methods. This article attempts a detailed analysis of the first series of letters of pope Gregory dedicated to the dispute and related to 595. These are letters to emperor Maurice (582–602), empress Constantina, the patriarch John IV of Constantinople, and the papal apocrisiary in Constantinople, deacon Sabinianus. The purpose of this study is to reconstruct pope Gregory’s argumentation system against the use of the Ecumenical title. Analysis. The author identifies several types of arguments that pope Gregory puts forward in his polemic against the title: canonical, biblical, dogmatic, ecclesiastical, political, pastoral and ascetic. Results. The article shows, on the one hand, what the letters have in common, and on the other, how the arguments of the pope vary depending on the recipient. Generally, pope Gregory expresses a sharply negative attitude to the title, and many researchers tend to see this fact as a contradiction to the concept of papal primacy, as it developed in a later period. Basing on the significant differences in argumentation between the letters to the emperor, the empress and the patriarch John – with the same purpose of all the messages – the article makes a conclusion about the care with which pope Gregory selects arguments. This can serve as one of the indirect indicators of the high importance of the dispute over the Ecumenical title for him, and also characterizes his perception of the idea of Church power in general.