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