The book deals with the "eternal" problems of linguistics: the problem of words and the problem of parts of speech. These problems have been facing European science for more than two millennia, but there is no theoretical unity in their interpretation; the numerous concepts of word and parts of speech that are available are diverse and often incomparable with each other. It seems that in order to solve the problem of "What is a word?" It is worth going beyond the limits of "pure" linguistics and turning to the study of the question of the psycholinguistic mechanism of man. The publication is designed for linguistic specialists, graduate students and philological students and everyone who is interested in theoretical problems of linguistics.