An idiom is a phrase that has a meaning that cannot be understood from the knowledge of its component parts. Linguists also use the word formative to describe idioms. Some idioms are extremely difficult to decode, but other are less opaque. Idioms are more easily understandable to those with more knowledge of the world and the culture from which the idiom comes.
Many idioms have their origins in metaphors. For example, to "bury the hatchet," "gnash one's teeth," and "give someone a piece of one's mind" are all rooted in metaphoric language. Some idioms have both a literal and an idiomatic meaning; only the context will determine the intended meaning. For example, to "pull someone's leg" and "kick the bucket" can be interpreted literally or metaphorically. If the literal meaning does not make any sense, such as "raining cats and dogs,", the phrase is likely to be an idiom.
Idioms can be phonologically irregular, calling for an emphasis on a word in the middle of the phrase instead of the end of the phrase. For example, "you can say that again" puts the emphasis on "that" rather than on "again." In spoken discourse, idioms are often indicated by a slight pause or an intake of breath. Additionally, speakers often first describe something in a non-idiomatic manner then repeat the same idea with an idiom.
Idioms usually evoke an image, such as to "pull someone's leg." E. Lattey (1986) found four categories of idioms that depict pictures. One type is those with a focus on the individual, such as to "die a thousand deaths." Another variety is those with a focus on the world, such as "that takes the cake." A third category contains those that refer to the interaction of individuals, such as to "lend someone a helping hand," and a fourth is idioms that describe the interaction between an individual and the world, such as "to know something inside and out."
R. Gibbs (1980) found that readers and listeners understand idioms as quickly as comparable literal expressions. In fact, highly familiar idioms are understood with more ease as idioms, than in their literal sense. That finding disproves the theory that idiomatic meanings are sought only if a linguistic analysis has failed. It might be that idioms are non-compositional items that must simply be retrieved from memory in order to be understood.
D. Swinney and A. Cutler (1979) postulated that idioms are recognized like other long words. When a listener hears an idiom, ordinary linguistic processing, plus retrieval from the phrasal lexicon, occur simultaneously. Usually, idiom retrieval occurs more quickly than literal expressions, because it does not require the lexical, syntactic and semantic processing involved in regular linguistic analysis.
R. Gibbs (1984) maintained that people can bypass literal meanings when they hear idioms, avoiding the step of linguistic analysis. She uses the relative speed of idiom comprehension to back her theory. Her theory is contradicted by the fact that many idioms have both literal and metaphorical meanings, so people must have to process idioms to determine which meaning to attribute.
Further disproving R. Gibbs's theory that linguistic processing of idioms is extraneous, idioms are not difficult to understand in novel formats. For example, "he didn't spill a single bean" is clearly understandable, even though it strays from its original form of "don't spill the beans." If the idiom were stored as a single retrievable phrase, people would have difficulty extracting meaning from alternate forms of the idioms.
Idioms can be useful to teachers of English to speakers of foreign languages. Many teachers of English as a Second Language avoid idioms and their complexity. However, idioms can make someone sound like a native speaker, and communicate a feeling or attitude toward an event in a way that literal phrases cannot. Idioms enliven speech, so native speakers use them frequently. Without the use of idioms, a foreigner speaking English will never "enter the spirit" of a foreign language.
In order to learn idioms, foreign language speakers have to progress through several challenging steps. They have to learn the meaning, as well as words that can be substituted for each part of the idiom. They have to learn the various constructions in which an idiom may appear. To fully understand idioms, they have to recognize the feelings and emotions, as well as cultural ideas that the phrases convey. In order to use idioms properly, they have to learn to choose idioms appropriate to the message they want to communicate, and to use them in the correct social circumstances.