In linguistics, free variation is the phenomenon of two (or more) sounds or forms appearing in the same environment without a change in meaning and without being considered incorrect by native speakers.
Sociolinguists argue that describing such variation as "free" is very often a misnomer, since variation between linguistic forms is usually constrained probabilistically by a range of systematic social and linguistic factors, not unconstrained as the term "free variation" suggests. The term remains in use in studies focused primarily on language as systems (e.g. phonology, morphology, syntax), however, since "[t]he fact that variation is 'free' does not imply that it is totally unpredictable, but only that no grammatical principles govern the distribution of variants.
When phonemes are in free variation, speakers are sometimes strongly aware of the fact (especially if such variation is noticeable only across a dialectal or sociolectal divide), and will note, for example, that tomato is pronounced differently in British and American English ( and respectively), or that either has two pronunciations that are distributed fairly randomly. However, only a very small proportion of English words show such variations. In the case of different realizations of the same phoneme, however, free variation is exceedingly common and, along with differing intonation patterns, variation in realization is the most important single feature in the characterization of regional accents.
English's deep orthography and the language's wide variety of accents often cause confusion, even for native speakers, on how written words should be pronounced. That allows for a significant degree of free variation to occur in English.
Pronunciation of many English words may vary depending on the dialect and the speaker. Although individual speakers may prefer one or the other pronunciation and one may be more common in some dialects than others, many forms can often be encountered within a single dialect and sometimes even within a single idiolect.