1. Subject of theoretical grammar. Analytic and synthetic word forms

6. The Modal Word
The modal word, occupying in the sentence a more pronounced or less
pronounced detached position, expresses the attitude of the speaker to the reflected
situation and its parts. Here belong the functional words of probability (probably,
perhaps, etc.), of qualitative evaluation (fortunately, unfortunately, luckily, etc.),
and also of affirmation and negation.
Modal words stand in a special relation to the sentence. They are not
sentence members, since giving an evaluation of the entire situation presented in
the sentence, they stand on the outside. For instance, in the sentence Perhaps,
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dimly, she saw the picture of a man walking up a road (Christie) the modal word
perhaps is not a sentence member, but if we remove it, the meaning of the
utterance will change – it will be just a statement of the fact.
Academician Shcherba states that there are some words that do not belong to
any part of speech. Prof. Ilyish regards the words yes, no and please as standing
outside the part of speech system. This point of view is also supported by Prof.
Smirnitsky.

8. Notional 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. The noun, for example, as a part of speech, is traditionally characterized by 1) the categorial meaning of substance (“thingness”), 2) a specific set of word-building affixes, the grammatical categories of number, case and article determination, prepositional connections and modification by an adjective, and 3) the substantive functions of subject, object or predicative in the sentence. In the same way, all the other notional parts of speech are described. Functional words, which include conjunctions, prepositions, articles, interjections, particles, and modal words, have incomplete nominative value, are unchangeable and fulfill mediatory, constructional syntactic functions.
In accordance with the said criteria, we can classify the words of the English
language into