On the other hand, oral or written speech lacking idioms loses much in expressiveness, colour and emotional force.
In modern linguistics, there is considerable confusion about the terminology associated with these word-groups. Most Russian scholars use the term "phraseological unit" ("фразеологическая единица") which was first introduced by Academician V.V.Vinogradov whose contribution to the theory of Russian phraseology cannot be overestimated. The term "idiom" widely used by western scholars has comparatively recently found its way into Russian phraseology but is applied mostly to only a certain type of phraseological unit as it will be clear from further explanations.
There are some other terms denoting more or less the same linguistic phenomenon: set-expressions, set-phrases, phrases, fixed word-groups, collocations.
The confusion in the terminology reflects insufficiency of positive or wholly reliable criteria by which phraseological units can be distinguished from "free" word-groups.
It should be pointed out at once that the "freedom" of free word-groups is relative and arbitrary. Nothing is entirely "free" in speech as its linear relationships are governed, restricted and regulated, on the one hand, by requirements of logic and common sense and, on the other, by the rules of grammar and combinability. One can speak of a black-eyed girl but not of a black-eyed table (unless in a piece of modernistic poetry where anything is possible). Also, to say the child was glad is quite correct, but a glad child is wrong because in Modern English glad is attributively used only with a very limited number of nouns (e. g. glad news), and names of persons are not among them.
Free word-groups are so called not because of any absolute freedom in using them but simply because they are each time built up a new in the speech process where-