Chapter II. Parts of speech and its types

1.3 Differences in the composition of grammatical categories and means of their expression in languages
While nouns have all three features of parts of speech - morphological, syntactic and semantic, and adjectives have a weaker morphological feature numerals are united only by their semantics .They denote the exact number or exact order; accordingly, they are subdivided into quantitative (one, two ...) and ordinal (the first, the second ...). They have no inflectional signs; syntactically, they can occupy positions characteristic of both nouns and adjectives:
She might be thirty or forty-five. (Christie) Two Italian primitives on the wall. (Christie) She had not seen me for four days. (Snow)
Pronouns have an extremely generalized meaning: they point to any objects, creatures, abstract concepts, without naming them. This is a highly generalized part of speech, actualized in the context, in the situation, but devoid of substantive real content in abstraction from the specific situation. Syntactically, pronouns function in the same way as nouns or adjectives.
Pronouns fall into a number of subclasses, different in lexical content, morphological forms and syntactic functions. The following subclasses are usually distinguished: personal, possessive, demonstrative, interrogative, reflexive, relative, indefinite, negative, indefinite personal pronouns. This classification, as B. A. Ilyish rightly points out, is entirely based on semantics. However, most of these semantic subclasses have some formal grammatical features[4].
Yu. S. Maslov defines a verb as a part of speech that expresses the grammatical meaning of an action, that is, a sign of a dynamic, flowing in time. The grammatical meaning of an action is understood broadly: it is not only an activity in the true sense of the word, but also a state and simply an indication that the given object exists, that it belongs to a certain class of objects (persons): A chair is a piece of furniture. He wrote a letter. He will soon recover. It is important that the verb conveys the sign not statically, not as a property attributed to the object (person), but as a sign that necessarily proceeds in some temporary (even if unlimited) period. This sign is not an abstract name for an action; the so-called personal (Finite) forms of the verb always convey the action as coming from a certain agent, therefore the syntactic function of the personal forms of the verb is unambiguous: they are always the predicate of the sentence.
Adverbs relatively late received an independent status of a significant part of speech in grammatical theory. Early grammarians (for example, G. Sweet) included them in the undivided category of "particles", which included all the invariable parts of speech. O. Jespersen also includes adverbs in the general group of particles, directly indicating that up, immediately, and. belong to the same group, for they do not belong to nouns, verbs, adjectives and pronouns. Jespersen, on the one hand, distinguishes prepositions, conjunctions and adverbs, on the other hand, combines them into one group. There is a clear contradiction here in Jespersen's system itself; in the theory of three ranks, the adverb usually takes the position of the second degree of subordination ("tertiary"), occasionally - the first degree of subordination ("secondary"), which is completely excluded for prepositions and conjunctions. In other words, in the theory of three ranks, the adverb occupies the position of a member of a sentence, or rather, a member of a phrase; at the same time, it is considered along with classes that are incapable of being members of a sentence [4].
The semantic classification of adverbs is very ramified and, like any semantic breakdown, to a certain extent allows for subjectivism. We accept the main classification adopted in Russian grammar - into qualitative and adverbial, and already within these groups we will point out possible semantic subgroups.
Modal words convey the subjective attitude of the speaker to the statement. For the first time, modal words were singled out in Russian linguistics; previously they were usually classified as adverbs. True, G. Sweet and E. Crazinga single out adverbs that refer to the entire sentence and convey the speaker's attitude to the stated fact. Thus, this type was also noted in foreign linguistics, but was not singled out as a special category.
Modal words can express certainty or conjecture, as well as a subjective assessment. So, the modal words certainly, of course, surely, really, indeed express confidence, perhaps, maybe, probably, possibly - uncertainty, presumption; fortunately, unfortunately, luckily, unluckily convey the speaker's view of the desirability or undesirability of this or that action.