The notion of “level”, generally accepted in , is very convenient for scientific linguistic research. The analysis requires that every language level should have its own unit. Naturally, the word combination is the smallest unit of the word combination level.

According to the deep-rooted tradition, a language unit may be con­sidered as such if and only if it is a component of a higher level. Thus, for example, phonemes are parts of units of a higher level, i.e. parts of mor­phemes. Therefore, phonemes may be treated as units of a level lower than that of morphemes.

The correlation of syntactic units, called “word combination” and “sen­tence”, is slightly different. The sentence is usually regarded as unit of a higher level than a word combination. Still, as some linguists point out, the word combination may function as a sentence or part of a sentence, while the sentence may be realized as word combination, a number of word com­binations, or a single word.