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

13 The dichotomy of language and speech
A dichotomy is any splitting of a whole into exactly two non-overlapping parts. In other words, it is a mutually exclusive bipartition of elements. i.e. nothing can belong simultaneously to both parts, and everything must belong to one part or the other. They are often contrasting and spoken of as "opposites." The term comes from dichotomos (divided): dich- ([in] two) temnein (to cut). The above applies directly when the term is used in mathematics, linguistics. For example, if there is a concept A, and it is split into parts B and not-B, then the parts form a dichotomy: they are mutually exclusive, since no part of B is contained in not-B and vice-versa, and they are jointly exhaustive, since they cover all of A, and together again give A.
One of the fundamental concepts of linguistics is the dichotomy of «language and speech» (langue—parole) introduced by F. de Saussure. According to it language is a system of elementary and complex signs-phonemes, morphemes, words, word combinations, utterances and combinations of utterances. Language as such a system exists m human minds only and linguistic forms or units can be systematise" into paradigms. language is a mentally organised system of linguistic units. An ъ0 .. aj speaker never uses it. When we use these units we mix m in acts of speech. As distinct from language speech is not relv mental phenomenon, not a system but a process of combining these linguistic elements into linear linguistic units that are called syntagmatic. The result of this process is the linear or syntagmatic combination of vowels and consonants into words, words into word-combinations and sentences and combination of sentences into texts.
14. The phrase. The problem of predicative phrases.
In everyday speech, a phrase may refer to any group of words. In linguistics, a phrase is a group of words (or sometimes a single word) that form a constituent and so function as a single unit in the syntax of asentence. A phrase is lower on the grammatical hierarchy than a clause.
We will term "phrase" every combination of two or more words which is a grammatical unit but is not an analytical form of some word (as, for instance, the perfect forms of verbs). The constituent elements of a phrase may belong to any part of speech. The difference between a phrase and a sentence is a fundamental one. A phrase is a means of naming some phenomena or processes, just as a word is. Each component of a phrase can undergo grammatical changes in accordance with grammatical categories represented in it, without destroying the identity of the phrase. For instance, in the phrase write letters the first component can change according to the verbal categories of tense, mood, etc., and the second component according to the category of number.