Comprehensive analysis of the mechanism of modalation of language units in Russian language includes research of the causes, prerequisites, conditions, steps and limits of their transposition from different parts of speech into interstitial class of parenthetic- modal words and expressions. It is important to establish the morphological base of the transpositional process of modalation. Studies show that verbs of different forms of representation can be used in the parenthetic-modal function, for example: (personal forms, infinitives, adverbial participles, short participles, e. g. you see, to tell the truth, considering..., apparently), both full and short adjectives, including those in impersonal-predicative position (indeed, my bad, it is said, it appears, etc.), adverbs (by the way, on the contrary, etc.), pronoun-adverbs (by no means), nouns (in truth, in fact, etc.), conjunctions (however) (see [2-8]).

Studying the mechanism of the modalation of adverbs is of great interest, indeed. In terms of structural-morphological correlativity with other word classes adverbs that are subject to modalation (vice versa, absolutely, then) can be divided into three groups (see [1, p. ] ):

Firstly, those are the adverbs derived from short adjectives in positive degree such as likely, absolutely (ending with -o and -e in Russian - похоже, бесспорно):

(1) (a) It was like a play (short adjective);

(b) He mimicked the neighbor kids very alike (adverb);

(c) He's likely been here before (parenthetic-modal word).

Secondly, those are the adverbs derived from adjectives in synthetic and analytical forms of the comparative degree (more accurately, more precisely, more quickly, more shortly, more exactly, etc.) and analytical form of the superlative degree (the most precisely, the most likely, etc.):

 (2) (а) You should express your thoughts more precisely (adverb); 

(b) The second expert report is more precise and accurate (adjective);

(c) The project's fate depended on him, more precisely, the fate of those who prepared it (parenthetic-modal word)

Thirdly, those are the adverbs formed from a combination of objective cases of nouns, adjectives, numerals and pronouns with prepositions (by the way, finally, additionally, vice versa, opposite, truly, in truth, probably, conjointly, later, then, in my opinion/mind, in your opinion/mind, etc.):

 (3) (a) And remember, that's a sure affair we're going to do! (adjective);

(b) For sure, you shouldn't listen to his blandishments (parenthetic-modal word).

Morphological foundations of the modalation of adverbs like by the way, truly, in truth are quite auspicious: just like parenthetic-modal words they can be characterized as inalterable. In general, we can distinguish two groups of adverbial word forms that are subject to modalation:

The first group includes such inalterable adverbs as contrarily, vice versa, by the way, by no means, later, in my mind/opinion, generally: they don't have the grammatical category of degrees of  comparison and thus when modalated they keep their feature of inalterability:

 (4)  He generally didn't like small talk--> Generally, legality of such actions is a separate topic;

(5) One couldn't tell for sure how many people were present --> The job, for sure, will be re-done;

The lack of an inflectional paradigm creates an auspicious morphological base for the adverbs of this type to be functionally and semantically converted when used as parenthetic-modal words.

The second group holds alterable adverbs that have the degrees of comparison like soon (sooner, the soonest), correctly (more correctly, the most correctly), accurately (more accurately, the most accurately), shortly (more shortly). At the same time, the presence of the inflectional paradigm is not an obstacle for their conversion into parenthetic-modal words. Some of them (correctly, accurately, shortly and others) are modalated in forms of positive, comparative and superlative degrees of comparison (correctly, more correctly, the most correctly; accurately, more accurately, the most accurately, etc.), and others (soon) - just in forms of the comparative and superlative degrees (sooner, the soonest; but soon).

Forms of the degrees of comparison of such adverbs can be affected by desemantization when used as parenthetic-modal words; their characteristic of alterability in this case becomes the characteristic of inalterability. Compare the following examples:

The sooner you start running, the sooner you'll get there (adverb soon in a comparative form with the meaning "faster") --> It's sooner just a mistake rather than someone's evil intent ("fixed" parenthetic-modal word in a subjective-modal meaning "probably"). Parenthetic-modal type of using such words can be appropriate to adverbs in all of the degrees of comparison. Adverbial lexeme probably/more probably/most probably is also of great interest because it's transposed into parenthetic-modal words and expressions with a meaning of persuasion. Compare the following:

 (6) (a) You are probably sick;

      (b) He kept silent or, more probably, pretended that he didn't hear anything;

       (c) Most probably, there are no chances to win.

As the foregoing material testifies, transpositional process of modalation includes adverbs of different morphological types, among them are those with word changing forms, i. e. having the paradigm of the category of the degrees of comparison. However, adverbs in parenthetic-modal position lose this grammatical category.

* The work is performed within the project "Complex research of modalation as a type of stepping transposition of language units in semantic syntactical category of introductory modal words", carried out with financial support of the Russian humanitarian scientific fund (grant No. 15-04-00039a).

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