The vocabulary of a language is enriched not only by words but also by phraseological units. Phraseological units are word-groups that cannot be made in the process of speech, they exist in the language as ready-made units. They are compiled in special dictionaries. The same as words phraseological units express a single notion and are used in a sentence as one part of it. American and British lexicographers call such units «idioms». We can mention such dictionaries as: L.Smith «Words and Idioms», V.Collins «A Book of English Idioms» etc. In these dictionaries we can find words, peculiar in their semantics (idiomatic), side by side with word-groups and sentences. In these dictionaries they are arranged, as a rule, into different semantic groups.
Phraseological units can be classified according to the ways they are formed, according to the degree of the motivation of their meaning, according to their structure and according to their part-of-speech meaning.
A.V. Koonin classified phraseological units according to the way they are formed. He pointed out primary and secondary ways of forming phraseological units.
Primary ways of forming phraseological units are those when a unit is formed on the basis of a free word-group :
a) The most productive in Modern English is the formation of phraseological units by means of transferring the meaning of terminological word-groups, e.g. in cosmic technique we can point out the following phrases: «launching pad» in its terminological meaning is «стартова площадка» , in its transferred meaning - «відправний пункт», «to link up» - «cтикуватися, стикувати космічні човни» in its tranformed meaning it means -«знайомитися»;
b) a large group of phraseological units was formed from free word groups by transforming their meaning, e.g. «granny farm» - «пансионат для старих людей», «Troyan horse» - «компьютерна програма, яка навмиснестворена для пвиведення з ладу компьютера»;
c) phraseological units can be formed by means of alliteration , e.g. «a sad sack» - «нещасний випадок», «culture vulture» - «людина, яка цікавиться мистецтвом», «fudge and nudge» - «ухильність».
d) they can be formed by means of expressiveness, especially it is characteristic for forming interjections, e.g. «My aunt!», « Hear, hear !» etc
e) they can be formed by means of distorting a word group, e.g. «odds and ends» was formed from «odd ends»,
f) they can be formed by using archaisms, e.g. «in brown study» means «in gloomy meditation» where both components preserve their archaic meanings,
g) they can be formed by using a sentence in a different sphere of life, e.g. «that cock won’t fight» can be used as a free word-group when it is used in sports (cock fighting ), it becomes a phraseological unit when it is used in everyday life, because it is used metaphorically,
h) they can be formed when we use some unreal image, e.g. «to have butterflies in the stomach» - «відчувати хвилювання», «to have green fingers» - «досягати успіхів як садовод-любитель» etc.
i) they can be formed by using expressions of writers or polititions in everyday life, e.g. «corridors of power» (Snow), «American dream» (Alby) «locust years» (Churchil) , «the winds of change» (Mc Millan).
Secondary ways of forming phraseological units are those when a phraseological unit is formed on the basis of another phraseological unit; they are:
a) conversion, e.g. «to vote with one’s feet» was converted into «vote with one’s
b) changing the grammar form, e.g. «Make hay while the sun shines» is transferred into a verbal phrase - «to make hay while the sun shines»;
c) analogy, e.g. «Curiosity killed the cat» was transferred into «Care killed the cat»;
d) contrast, e.g. «cold surgery» - «a planned before operation» was formed by contrasting it with «acute surgery», «thin cat» - «a poor person» was formed by contrasting it with «fat cat»;
e) shortening of proverbs or sayings e.g. from the proverb «You can’t make a silk purse out of a sow’s ear» by means of clipping the middle of it the phraseological unit «to make a sow’s ear» was formed with the meaning «помилятись».
f) borrowing phraseological units from other languages, either as translation loans, e.g. « living space» (German), « to take the bull by the horns» (Latin) or by means of phonetic borrowings «meche blanche» (French), «corpse d’elite» (French), «sotto voce» (Italian) etc.
Phonetic borrowings among phraseological units refer to the bookish style and are not used very often.
There are diffrenent combinations of words. Some of them are free, e.g. to read books (news papers, a letter, etc.) others are fixed, limited in their combinative power, e.g. to go to bed, to make a report. The combinations of words which are fixed (set-expressions) are called phraseological units.