Absolutely everything is divided into categories in the Russian language. Part of speech is determined by morphological features, syntactic function and lexical meaning.
Their composition was formed all the time while the grammar of the Russian language was developing. At the present stage, independent parts of speech (full-valued) and official are distinguished. Interjections, modal words and onomatopoeic are considered separately.
The independent parts of speech (in some sources they are also called significant) indicate objects, quantity, properties, action, quality, condition. They have a grammatical and lexical meaning. In addition, they perform a syntactic function, acting in the sentence as the main or secondary member.
The independent parts of speech consist of seven categories of words: numeral, adjective and noun, verb, pronoun, adverb and category of state. Not all of them can change their shape using a variety of means. This ability is characteristic only of adjectives, nouns, numerals, as well as verbs and pronouns. The category of condition (lack of time, sorry, glad) and adverbs do not have the means forming various forms. A minor exception is made up of qualitative adverbs that can create degrees of comparison.
The category of state (or predicate) should be considered separately, since it is not distinguished in all grammars. For the first time this was done by V.V. Vinogradov and L.V. Shcherba. Moreover, the understanding of the predicate is narrow and wide. In the first case, the category of state includes only those words that in the impersonal sentence (also in the one where the main term is expressed by the infinitive) play the syntactic role of the predicate: sunny, cold, hard to understand, you can’t keep quiet, once, you can agree, it's damp, warm . In the second case, the category of state includes all words that are not verbs, but act as a predicate: you can’t, just right, you should, I’m glad, obliged, you can, at the ready.
Grammatical signs of a predicate: use with a bunch and the meaning of a condition. In the case of a narrow understanding, the immutability of the word is added here.
There is a lot of special literature, which quite convincingly substantiates the categorization of the state category as parts of speech. Indeed, there are words in the language that are not verbs, but fulfill the syntactic function of the predicate, like verbs. Some linguists associate the concept of a category of state with the function of non-verbal word forms in a sentence. But, nevertheless, this issue is still problematic and remains open.
The accepted distribution of parts of speech cannot be considered constant, since in a language there often occurs a transition of tokens from one part of speech to another. However, not all words can do this freely. Some independent parts of speech more often pass into other independent, less often - in the service. For example, adverbs can go into the category of prepositions: around, around. The meaning of pronouns appears in nouns : Case (it) was in the fall. The participles pass into prepositions and dialects: despite, thanks, sitting, silently, standing. Often nouns become parts of complex conjunctions, particles of prepositions: is it a joke, for, while, etc.
Parts of speech in English, as well as in Russian, are divided into full-valued (significant, independent) and official. The first also includes those words that have a full lexical meaning, are members of a sentence and call actions, signs and objects. English grammar refers to them adverb, verb, pronoun and adjective, noun and numeral.