Branches of linguistics. Synchronic vs diachronic approaches to the language study. Lexicology – ‘the science of the word’

According to the parts of speech of the summit constituents, two-summit units are subdivided into:
-attribute-substantive units equivalent to nouns, e.g. black art, couch potato, dark horse, Dutch courage, rough diamond etc.;
-verb-substantive units equivalent to verbs, e.g. to take the floor, to break the ice, to lose one’s heart, not to lift a finger etc.;
-phraseological repetions equivalent to adverbs, e.g. now and never etc.;
-adverbial multi-summit unts, e.g. every other day etc.
The Structural-Semantic Classification
Prof. Alexander V. Kunin Английская фразеология (1970)
-Phraseology is regarded as a self-contained branch of linguistics and not as part of lexicology.
-Phraseology deals with a phraseological subsystem of the language and not with isolated PhU.
-Phraseology is concerned with all types of set expressions.
-Semantically set expressions fall into phraseological units with fully or partially transferred meanings, phraseomatic units with components used in their literal meanings and border-line cases.
-Phraseological and phraseomatic units are not regarded as word-equivalents, but some of them are treated as word correlates.
-Set-expressions are ready-made units not created in speech; they are not elements of individual style but language units; they are characterised by lexical and semantic stability.
According to the communicative function determined by their structural-semantic features four classes of set-expressions are defined:
nominating units denote extralingual entities, e.g. as the crow flies;
nominating-communicative verbal phrases can be transformed into a sentence when used in the passive voice, e.g. to break the ice – the ice is broken; to pull somebody’s leg – somebody’s leg is pulled.
interjectional units express emotions, e.g. a pretty kettle of fish, by George!
communicative units are proverbs, sayings, quotations whose structure is similar to that of a sentence, e.g. Familiarity breeds contempt.