Structural completeness of linear language organization is provided in two ways: by means of substitution and representation. Substitution is based on inclusion of a unit that replaces the unit mentioned before in order to avoid repetition as well as for the sake of brevity: the substituting unit may be much shorter than the substituted one, a single element may substitute for the whole group. Thus, substitution is always based on anaphora, since it should be correlated with the element given before.

There are a number of language elements capable of functioning as sub­stitutes. Each morphological class has its own substituting units. For exam­ple, to replace nouns, the word one is the most frequent: an English book and several German ones; he is a doctor and his wife is one, too. As some linguists note, the word one is also capable of substituting for nouns, used to deliver identifying meaning. Such use requires the singular form: Such a question is an inevitable one.

Most linguists, Western ones in particular, treat third person personal pronouns singular and plural as substitutes. These words, too, function in text anaphorically, just like the substitute one. Unlike one, however, the third person pronouns replace the whole nounal group, i.e. including its at­tributive components: cf. a blue pencil and five black ones vs John and Sandra s bedroom is the coziest in the house. It is exquisitely furnished.

Besides personal pronouns, the function of substitution may be per­formed by demonstrative pronouns that/those: The best fruits are those from the Crimea; Which shirt would you prefer? – I’d rather buy that of pure cotton.

Notional words are usually replaced by the verb do: Jill sings better than I do; Jeremy went to bed late, so did we.

When other parts of speech are concerned, substitution is not so explicit, though it does exist. For example, an adjective in the predicative position may be replaced by the word so: Mary is smart, but her daughter is still more so; Is she happy? – Yes, very much so.

Representation differs from substitution in that it does not presuppose introduction of any new element into the construction. What it means is using only a part of the construction pronounced previously: I have nev­er ridden a horse but I’d love to. The pre-Infinitive particle to represents the whole group to ride a horse. Though the rest of the structure remains implied, the group expressed by to is structurally complete and presents a grammatical construction. It should be noted, though, that while groups with words-substitutes may function as grammatically independent units (a black one), groups with representatives cannot exist independently, without correlating with the represented structure.