In linguistics, an idiolect [id-ee-uh-lekt] is a variety of a language unique to one individual person. It is manifested by patterns of vocabulary or idiom selection (the individual’s lexicon), grammar, or pronunciations that are unique to the individual. Every individual’s language production is in some sense unique.
Linguists disagree about exactly what is shared, in terms of the underlying knowledge of the language, among speakers of the same language or dialect. According to this view, a language is an ‘ensemble of idiolects… rather than an entity per se.’
This contrasts with a view among non-linguists that languages as ideal systems exist outside the actual practice of language users. They believe that there is one ‘correct’ pattern of grammar and vocabulary that underlies Standard English, and that individual usage derives from this external system.
Linguists who understand particular languages as a composite of unique, individual idiolects must nonetheless account for the fact that members of large speech communities, and even speakers of different dialects of the same language, can understand one another. All human beings seem to produce language in essentially the same way. This has led to searches for universal grammar, as well as to attempts to define the nature of particular languages.
The scope of forensic linguistics includes attempts to identify whether a certain person did or did not produce a given text by comparing the style of the text with the idiolect of the individual. The forensic linguist may conclude that the text is consistent with the individual, rule out the individual as the author, or deem the comparison inconclusive.