The article is devoted to the grammatical study of the parts of speech of by outstanding domestic scientist – Professor I. Kucherenko. Professor I. Kucherenko laid out the key points of this teaching in the fundamental two-volume treatise “Theoretical Issues of the Grammar of the Ukrainian Language: Morphology”, where he substantiated the logical grammatical paradigmatic system of the Ukrainian language with impeccable clarity, while at the same time proposing to solve the most difficult and controversial issues in the field of semasiology, syntax, and communicative linguistics. Having been printed in early (the 60s of the 20th century), this work became a significant achievement of Slavic linguistics and largely determines the development of grammatical thought in Ukraine to this day. The scientist’s classification approach is focused on the “unequivocal (monistic)” criterion, namely the lexical meaning of the word, which the scientist sometimes calls “real”. The lexical meaning of a word reflects the conceptual, communicative and cognitive nature of a linguistic sign and determines its grammatical attributes, not vice versa. The use of a multi-valued criterion, which is widespread in grammars to this day, turns into a gross violation of logic, makes it impossible to clearly differentiate common and distinctive, basic (generic) and secondary (specific) features of word classes. As a result, words are forced into categories where they are “foreign”, such as, for example, participles among verbs. Professor I. Kucherenko is the first to substantiate the feasibility of considering participles, as well as so-called ordinal numerals, as well as adjectival classes of pronominal words in the adjective category. The lexical meaning of a word determines its typified function in a sentence, which (sentence), according to the scientist, is not only the main unit of syntax, but also a “real unit” among the rest of the linguistic units. The scientist interprets the concept of “real” as something that does not exist in registers or nomenclature, but provides communication and knowledge. Thus, while developing theoretical grammar, Professor I. Kucherenko showed foresight in terms of the categories of cognitive linguistics and communicative syntax, many decades ahead of his contemporary scientific thought. Approaches to the so-called service parts of speech are significant in the paradigmatic teaching of Professor I. Kucherenko. The scientist rejects the terminological dichotomy “meaning-bearing / non- meaning-bearing”, justifiably believing that there is no primary and secondary in the lexical material. It visualizes the understanding that prepositions, conjunctions, particles ensure the movement of thought from sensual contents to the sphere of abstract thinking, reflecting the facts of human mental activity, which is the same reality as the naming of visible (gross) material objects of the world. In this connection, the scientist develops the proposal about synsemantics and three levels of semantics (defined, generalized, generalized and indicative).