This article is devoted to the analysis of the evolution of the linguistic views of A. Krymskyi in the process of his scientific communication with B. Grinchenko, P. Zhytetskyi and I. Franko (late XIX – early XX centuries). Different contradictory moments in the scientific researches of linguists from the different regions of Ukraine during the period of formation of the Ukrainian literary language were revealed. Various issues of linguistic discussions during the late XIX – early XX centuries, in which prominent linguists from Galicia and Upper Dnieper Ukraine participated, are characterized. In this context, the most interesting in terms of coverage of various linguistic problems was the correspondence of A. Krymskyi with B. Grinchenko, which lasted for seventeen years (1891–1908). The attitude of scholars to the formation of the criteria of literary word usage and principles of language formation is clarified. It was found out that the main criteria for correct word usage for linguists of Upper Dnieper Ukraine was the presence of a word in the vernacular language and in literary texts, which is confirmed by the materials of the first academic Russian-Ukrainian dictionary edited by A. Krymskyi (1924–1933) and the Dictionary of Ukrainian language compiled by B. Grinchenko (1907–1909). The scientific value of different linguistic ideas expressed by these scholars in their epistolary, especially on the usage of individual words and grammatical forms, as well as the ways of development of Ukrainian literary language, was noted. Their views on formation of the single version of literary language based on the language use of Upper Dnieper Ukraine are outlined. The desire of these linguists to promote the unification of the norms of the Ukrainian language through the creation of grammatical and lexicographical works is characterized. Based on the analysis of epistolary texts by A. Krymskyi and B. Grinchenko, it is stated out that their ideas contributed to the emergence of valuable grammatical and lexicographical works that contain huge lexical and phraseological material from the Ukrainian classical literature and folklore sources. The fruitful scientific and literary work of these scholars became an integral component of the process of development and unification of literary norms of Ukrainian language.