An interesting paradox is that the Greek tradition is considered in the West as the source of Western linguistics, and in Russia as the source of Russian linguistics, whereas the Russian tradition is said to be entirely different from the Western one by many Russian scholars. It is held in this paper that the notion of grammatical tradition is of no use in the history of grammars. As a matter of fact, what is at stake in the Middle Ages is a deep rooted opposition between a rationalist and anti-rationalist (fideist) approach of grammar, both in the West and in the Orthodox Slavic world: grammar is made either to generate new texts or to repeat old ones. The history of medieval religious struggles in the East slavic world is a fascinating source for studying the ideologies underlying gramatical debates.