The description of Armenian grammar has a long history. Several decades after the creation of the Armenian alphabet by Mesrop Mashtots, in all probability in the late 5^th century, the Art of Grammar of Dionysius Thrax was translated from Greek, and 12 commentaries on it were written until the late 16^th century. This translation, which laid the foundation of Armenian grammatical terminology, and its commentaries artificially ascribed some features of Greek to Armenian. In the 1340s Yovhannēs wrote a different work entitled On Grammar, extant in a single manuscript copied in 1350. In 1333–1347 he was the head of the catholic monastery in Kʻṙna in the Armenian province Nakhijevan, founded by catholic missionaries sent to Eastern Armenia by the pope and their Armenian cooperators, the Fratres Unitores. The section on phonetics in this work is strongly influenced by the Armenian version of Dionysius, and the terms for parts of speech and many grammatical categories are borrowed from it. But Yovhannēs also used Latin sources and dedicated the two last sections of his work to syntax. He mentions the name of Priscian (6^th c.), and his work also has parallels with the commentaries on Priscian’s work, in particular, with Summa super Priscianum by Petrus Helias (12^th c.). He translated some phrases, mainly definitions, from these sources, distinguished between the substantives and the adjectives in the section “On the Noun”, described verbal tenses and voices in a more reliable way, introduced the notions and terms for the sentence and its varieties, for government, and mentioned grammatical agreement. Nevertheless, the work On Grammar also features the author’s independent observations. It is written in classical Grabar, but some examples are given in Middle Armenian.