1. the subject of theoretical grammar its relations to other branches of linguistics

12 Language as a system and structure
Language is the system, phonological, lexical, and grammatical, which lies at the base of all speaking. It is the source which every speaker and writer has to draw upon if he is to be understood by other speakers of the language.
Language is regarded as a system of elements (or: signs, units) such as sounds, words, etc. System implies the characterization of a complex object as made up of separate parts (e.g. the system of sounds). Language is a structural system. Structure means hierarchical layering of parts in `constituting the whole. In the structure of language there are four main structural levels: phonological, morphological, syntactical and supersyntatical. The levels are represented by the corresponding level units:
The phonological level is the lowest level. The phonological level unit is the`phoneme. It is a distinctive unit (bag – back).
The morphological level has two level units:
the `morpheme – the lowest meaningful unit (teach – teacher);
the word - the main naming (`nominative) unit of language.
The syntactical level has two level units as well:
the word-group – the dependent syntactic unit;the sentence – the main communicative unit.
The supersyntactical level has the text as its level unit.
As a system, language is subdivided into three basic subsystems, each of which is a system in its own turn. They are the phonetical (phonological), lexical and grammatical systems. The phonetical system includes the material units of which language is made up: sounds, phonemes, different intonation models, and accent models. The phonetical system of language is studied by a separate branch of linguistics called phonology. The lexical system includes all the nominative (naming) means of language – words and stable word-combinations. The lexical system is studied by lexicology. The grammatical system includes the rules and regularities of using lingual units in the construction of utterances in the process of human communication. The grammatical system is described by grammar as a branch of linguistics