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

The Functional Classification
Prof. Alexander I. Smirnitskiy Лексикология английского языка (1956)
-the functional approach proceeds from the assumption that PhU may be defined as non-motivated word-groups functioning as word-equivalents;
-the functional approach seeks to establish formal criteria of idiomaticity by analysing the syntactic functions of PhU by analysing the syntactic function of PhU in speech;
-semantic inseparability and grammatical inseparability of PhU are viewed as the aspects of idiomaticity which enables to regard them semantically and grammatically equivalent to single words;
-PhUn are characterised by a single stylistic reference irrespective of the number and nature of the component words.
Phraseological units vs idioms proper
-PhU are non-motivated word-groups functioning as word-equivalents by virtue of their semantic and grammatical inseparability.
-Idioms proper (proverbs, sayings and quotations) are ready-made expressions with a specialised meaning of their own which cannot be inferred from the meaning of their components taken singly; they do not always function as word-equivalents.
According to the number and semantic significance of their constituent parts, PhU are classified into:
-one-summit (одновершинные) units, which have one meaningful component;
-two-summit and multi-summit (двухвершинные или многовершинные), which have two or more meaningful constituents.
According to the parts of speech of the summit constituents, one-summit units are subdivided into:
-verbal-adverbial units, the semantic and grammatical centres are in the first component, e.g. to give up, to put through, to get up etc.;
-units equivalent to verbs, their semantic centre being in the second component and the grammatical centre – in the first one, e.g. to be surprised, to be tired etc.; --prepositional-substantive units equivalent either to adverbs or to copulas, their semantic centre being in the nominal constituent and no grammatical centre, e.g. by heart, by means of etc.