Notional words and functional words

Traditionally, all parts of speech are subdivided on the upper level of classification into notional words and functional words. Notional words, which traditionally include nouns, verbs, adjectives, adverbs, pronouns and numerals, have complete nominative meanings, are in most cases changeable and fulfill self-dependent syntactic functions in the sentence. Functional words, which include conjunctions, prepositions, articles, interjections, particles, and modal words, have incomplete nominative value, are unchangeable and fulfill mediatory, constructional syntactic functions.

There are certain limitations and controversial points in the traditional classification of parts of speech, which make some linguists doubt its scientific credibility. First of all, the three criteria turn out to be relevant only for the subdivision of notional words. As for functional words, they are rather characterized by the absence of all three criteria in any generalized form. Second, the status of pronouns and the numerals, which in the traditional classification are listed as notional, is also questionable, since they do not have any syntactic functions of their own, but rather different groups inside these two classes resemble in their formal and functional properties different notional parts of speech: e.g., cardinal numerals function as substantives, while ordinal numerals function as adjectives; the same can be said about personal pronouns and possessive pronouns. Third, it is very difficult to draw rigorous borderlines between different classes of words, because there are always phenomena that are indistinguishable in their status. E.g., non-finite forms of verbs, such as the infinitive, the gerund, participles I and II are actually verbal forms, but lack some of the characteristics of the verb: they have no person or number forms, no tense or mood forms, and what is even more important, they never perform the characteristic verbal function, that of a predicate. Equally dubious is the part-of-speech characterization of auxiliary verbs, intensifying adverbs, conjunctive adverbs and pronouns, and of many other groups of words which have the morphological characteristics of notional words, but perform mediatory constructional functions in a sentence, like functional words. There are even words that defy any classification at all; for example, many linguists doubt whether the words of agreement and disagreement, yes and no, can occupy any position in the classification of parts of speech.