Phraseology is a branch of lexicology studying phraseological units (set expressions, praseologisms, or idioms (in foreign linguistics). Phraseological units differ from free word-groups semantically and structurally: 1) they convey a single concept and their meaning is idiomatic, i.e. it is not a mere total of the meanings of their components 2) they are characterized by structural invariability (no word can be substituted for any component of a phraseological unit without destroying its sense (to have a bee in one’s bonnet (not cap or hat). 3) they are not created in speech but used as ready-made units. Unlike a word, a phraseological unit can be divided into separately structured elements and transformed syntactically (On the instant he was thinking how natural and unaffected her manner was now that the ice between them had been broken. (Th. Dreiser, ‘An American Tragedy’). I... found this man in a kind of seizure, and went for help. This broke the ice between us, and we grew quite chatty, without either of us knowing the other's name. (H. Pollitt, ‘Serving My Time’).
Phraseological units are classified in accordance with several criteria.
In the classification proposed by acad. Vinogradov phraseological units are classified according to the semantic principle, and namely to the degree of motivation of meaning, i.e. the relationship between the meaning of the whole unit and the meaning of its components. Three groups are distinguished: phraseological fusions (сращения), phraseological unities (единства), phraseological combinations (сочетания).
1. Phraseological fusions are non-motivated. The meaning of the whole is not deduced from the meanings of the components: to kiss the hare’s foot (опаздывать), to kick the bucket (сыграть в ящик), the king’s picture (фальшивая монета)
2. Phraseological unities are motivated through the image expressed in the whole construction, the metaphores on which they are based are transparent: to turn over a new leaf, to dance on a tight rope.
3. Phraseological combinations are motivated; one of their components is used in its direct meaning while the other can be used figuratively: bosom friend, to get in touch with.
Prof. Smirnitsky classifies phraseological units according to the functional principle. Two groups are distinguished: phraseological units and idioms.
Phraseological units are neutral, non-metaphorical when compared to idioms: get up, fall asleep, to take to drinking. Idioms are metaphoric, stylistically coloured: to take the bull by the horns, to beat about the bush, to bark up the wrong tree.
Structurally prof. Smirnitsky distinguishes one-summit (one-member) and many-summit (two-member, three-member, etc.) phraseological units, depending on the number of notional words: against the grain (не по душе), to carry the day (выйти победителем), to have all one’s eggs in one basket.
Prof. Amosova classifies phraseological units according to the type of context. Phraseological units are marked by fixed (permanent) context, which can’t be changed: French leave (but not Spanish or Russian). Two groups are singled out: phrasemes and idioms.
1. Prasemes consist of two components one of which is praseologically bound, the second serves as the determining context: green eye (ревнивый взгляд), green hand (неопытный работник), green years (юные годы), green wound (незажившая рана), etc.
2. Idioms are characterized by idiomaticity: their meaning is created by the whole group and is not a mere combination of the meanings of its components: red tape (бюрократическая волокита), mare’s nest (нонсенс), to pin one’s heart on one’s sleeve (не скрывать своих чувств).
Prof. Koonin’s classification is based on the function of the phraseological unit in communication. Phraseological units are classified into: nominative, nominative-communicative, interjectional, communicative.
1. Nominative phraseological units are units denoting objects, phenomena, actions, states, qualities. They can be:
a) substantive – a snake in the grass (змея подколодная), a bitter pill to swallow;
b) adjectival – long in the tooth (старый);
c) adverbial – out of a blue sky, as quick as a flash;
d) prepositional – with an eye to (с намерением), at the head of.
2. Nominative-communicative units contain a verb: to dance on a volcano, to set the Thames on fire (сделать что-то необычное), to know which side one's bread is buttered, to make (someone) turn (over) in his grave, to put the hat on smb’s misery (в довершение всех его бед).
3. Interjectional phraseological units express the speaker’s emotions and attitude to things: A pretty kettle of fish! (хорошенькое дельце), Good God! God damn it! Like hell!
4. Communicative phraseological units are represented by provebs (An hour in the morning is worth two in the evening; Never say “never”) and sayings. Sayings, unlike provebs, are not evaluative and didactic: That’s another pair of shoes! It’s a small world.
Some linguists (N.N. Amosova, J. Casares) don’t include proverbs and sayings into their classifications. Others (I.V. Arnold, A.V. Koonin, V.V. Vinogradov) do, on the grounds that 1) like in phraseological units their components are never changed 2) phraseological units are often formed on the basis of proverbs and sayings (A drowning man will clutch at a straw → to clutch at a straw).
In dictionaries of idioms the traditional and oldest principle for classifying phraseological units – the thematic principle – is used.