Idioms are usually rather informal and include an element of personal comment on the situation. They are sometimes humorous or ironic. That’s why we must be careful using them. It’s not a good idea to use them just to sound «fluent» or «good at English’. In a formal situation we can’t say: «How do you do, Mrs Watson. Do take the weight off your feet.» (sit down) instead of «Do sit down» or «Have a seat». It is important to know that their grammar is flexible. Some are more fixed than others. For instance, «barking up the wrong tree» (be mistaken) is always used in continuous, not simple form, e.g. I think you’re barking up the wrong tree. Generally, set expression, for example, come to the wrong shop, go the way of all flesh, make somebody’s blood boil, are idiomatical, they are also named phraseological. Besides, there are set expression such as pay a visit, make one’s appearance, give help. Their interpretation is disputable. Some linguists consider them to be a not idiomatical part of phraseology, which is opposed to idiomatical. If the expression is idiomatical, then we must consider its components in the aggregate, not separately [Каменецкайте 1971:3]. Idioms are a part of our daily speech. They give expressiveness and exactness to oral and written language. It’s not easy to master idioms fluently [Cудзиловский 1973:7]. Word — for — word translation can change the meaning of the idiom. The following sentences contain idioms:
1. She is pulling my leg. — to pull someone's leg means to trick them by telling them something untrue.
2. When will you drop them a line? — to drop someone a line means to send a note to someone.
3. I can't keep my head above water. — to keep one's head above water means to manage a situation.
4. It's raining cats and dogs. — to rain cats and dogs means to rain very heavily (a downpour).
5. Oh no! You spilled the beans! — to spill the beans means to let out a secret.
6. Why are you feeling blue? — to feel blue means to feel sad.
7. That jacket costs an arm and a leg. — an arm and a leg means something is very expensive.
Each of the word combinations in bold has at least two meanings: a literal meaning and a figurative meaning. Such expressions that are typical for a language can appear as words, combinations of words, phrases, entire clauses, and entire sentences. Idiomatic expressions in the form of entire sentences are called proverbs if they refer to a universal truth.
8. The devil is in the details.
9. The early bird catches the worm.
Proverbs such as these have figurative meaning. When one says "The devil is in the details", one is not expressing a belief in demons, but rather one means that things may look good on the surface, but upon scrutiny, problems are revealed.
Many idiomatic expressions in their original use were not figurative but had literal meaning.
For instance: «spill the beans» meaning to let out a secret probably originates in a physical spilling of beans which are either being eaten or measured out. The point is that the spiller certainly does not want to lose any beans.
«Let the cat out of the bag» has a meaning similar to the former, but the secret revealed in this case will likely cause some problems. A cat was sometimes put in bags to keep it under control or to pretend that it was a more saleable animal, such as a pig or a rabbit. So, to let the cat out of the bag suggests either that the ruse is revealed or that the situation is out of control.
«Break a leg» meaning good luck in a performance/presentation etc. This common idiom comes from superstition. It was thought that there were gremlins or sprites, little fairy-like creatures, backstage in theaters who would do exactly the opposite of whatever they were told. To say break a leg was to ensure the sprites would not in fact do the performers any damage.
Changes in the semantic structure of the components are of different nature. Some of them are metaphoric, others are metonymic, still others are based on illogical assumptions. They are like ships that pass in the night, on the tip of the tongue, once in a blue moon. There are others factors that are relevant in constructing a set phrase: rhythm, rhyme, alliteration, pun, contrast (out of sight, out of mind, head over heels, rain or snow).
According to Rosamund Moon, idiom is an ambiguous term, used in conflicting ways. In general use, idiom has two main meanings. First, idiom is a particular manner of expressing something in language, music, art, and so on, which characterizes a person or group within a community. Secondly, (and much less commonly in English), an idiom is a particular lexical collocation or phrasal lexeme, peculiar to a language.
Three principal factors are taken into account: institutionalization, lexico-grammatical fixedness, and non-compositionality. Institutionalization is the process by which a string or formulation becomes recognized and accepted as a lexical item of the language and passim): it is a necessary but not sufficient condition for a string to be classifiable as a fixed expression. Lexicogrammatical fixedness implies some degree of lexicogrammatical defectiveness in units, for example with preferred lexical realizations and often restrictions on aspect, mood, or voice. The non-compositionality of a string may be considered a semantic criterion. Yet sometimes the meaning of the whole unity of an idiom does not yield to its word-by-word interpretation of the string [Moon 1998:3-8].
One of the biggest obstacles to language learners is to master all idioms as there are too many of them. Sometimes some idioms cannot be understood literally. Even if the meanings of all the words in an idiomatic phrase as well as its grammar are simple, the meanings of the whole phrase may still be confusing due to cultural barriers, as in to set the Thames on fire. Therefore, a profound insight in idioms requires socio-cultural competence to offer language learners not only fun but also success in communication as language is learnt through culture and culture is learnt through language.