In linguistics, an accent is a manner of pronunciation of a language. Accents can be confused with dialects which are varieties of language differing in vocabulary, syntax, and morphology, as well as pronunciation. Dialects are usually spoken by a group united by geography or social status.
Children are able to take on accents quickly; children of traveling families, for example, can change their accents within a short period of time. This generally remains true until a person's early twenties, after which, a person's accent seems to become more entrenched.
All the same, accents are not fixed even in adulthood. An acoustic analysis by Jonathan Harrington of Queen Elizabeth II's Royal Christmas Messages revealed that the speech patterns of even so conservative a figure as a monarch can continue to change over her lifetime.
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As human beings spread out into isolated communities, stresses and peculiarities develop. Over time these can develop into identifiable accents. In North America, the interaction of people from many ethnic backgrounds contributed to the formation of the different varieties of North American accents. It is difficult to measure or predict how long it takes an accent to formulate. Accents in the USA, Canada and Australia, for example, developed from the combinations of different accents and languages in various societies, and the effect of this on the various pronunciations of the British settlers, yet North American accents remain more distant, either as a result of time or of external or "foreign" linguistic interaction, such as the Italian accent. It has been theorized that the accents of certain groups in the USA today resemble the English spoken by the settlers in the 17th and 18th centuries more than it does the English spoken by most Britons today.
In many cases, the accents of non-English settlers from Great Britain and Ireland affected the accents of the different colonies quite differently. Irish, Scottish and Welsh immigrants had accents which greatly affected the vowel pronunciation of certain areas of Australia and Canada.
When a group defines a standard pronunciation, speakers who deviate from it are often said to "speak with an accent". People from the United States would "speak with an accent" from the point of view of an Australian, and vice versa. Accents such as BBC English or General American may sometimes be erroneously designated in their countries of origin as "accentless" to indicate that they offer no obvious clue to the speaker's regional background.
Groups sharing an identifiable accent may be defined by any of a wide variety of common traits. An accent may be associated with the region in which its speakers reside (a geographical accent), the socio-economic status of its speakers, their ethnicity, their caste or social class, their first language (when the language in which the accent is heard is not their native language), and so on.
Certain accents are perceived to carry more prestige in a society than other accents. This is often due to their association with the elite part of society. For example in the United Kingdom, Received Pronunciation of the English language is associated with the traditional upper class. 
Actors are often called upon to speak varieties of language other than their own. For example, Missouri-born actor Dick van Dyke imitated a cockney accent in the film Mary Poppins. Similarly, an actor may portray a character of some nationality other than his or her own by adopting into the native language the phonological profile typical of the nationality to be portrayed -- what is commonly called "speaking with an accent". One example would be Viggo Mortensen's use of a Russian accent in his portrayal of Nikolai in the movie Eastern Promises.
An imitated accent rarely sounds accurate to the native speakers of the accent. The perception or sensitivity of others to accents means that generalizations are passed off as acceptable, such as Brad Pitt's Jamaican accent in Meet Joe Black. Angelina Jolie attempted a Greek accent in the film Alexander that was said by critics to be distracting. Gary Oldman has become known for playing eccentrics and for his mastery of accents.
Accents may have associations and implications for an audience. For example, in Disney films from the 1990s onward, English accents are generally employed to serve one of two purposes: slapstick comedy or evil genius. Examples include Aladdin (the Sultan and Jafar, respectively), The Lion King (Zazu and Scar, respectively), The Hunchback of Notre Dame (Victor the Gargoyle and Frollo, respectively), and Pocahontas (Wiggins and Ratcliffe, respectively - both of whom happen to be played by the same actor, American David Ogden Stiers).
Kentucky's highest court in the case of Clifford vs. Commonwealth held that a white police officer, who had not seen the black defendant allegedly involved in a drug transaction, could, nevertheless, identify him as a participant by saying that a voice on an audiotape "sounded black." The police officer based this "identification" on the fact that the defendant was the only African American man in the room at the time of the transaction and that an audio-tape contained the voice of a man the officer said “sounded black” selling crack cocaine to a white informant planted by the police.