In the early stages of learning a foreign language, it is easy to believe that all we need to do is to master the rules of grammar, learn some vocabulary, and try to pronounce everything such that native speakers will hopefully understand us. These tasks keep us fairly well occupied until we spend some time in a country where the language is spoken. There we often realise that things are not as simple as we might have thought, since native speakers do not always seem to use the kind of language we have been learning. Frequently, they appear to break the rules of grammar we have so arduously internalised; they use words in ways we have not encountered before; and, most noticeably perhaps, their pronunciation of those words does not always coincide with the pronunciation we have been taught.

What the foreign language learner finds in such situations is known in linguistics as variation. By this, we mean that the vocabulary, grammar and pronunciation of any language will vary according to who is communicating with whom, in what situation and on what topic. By contrast, the kind of language we learn in the classroom is, of necessity, more uniform. This is because most teaching and learning is based on what is considered to be the standard variety of the foreign language in question.