In any speech community observed over a period of time suitable for analysis, the forms and meanings of the language(s) in use exhibit variation, i. e., elements and relations among them that are held in some sense to be ‘the same’ appear sometimes in one way sometimes in another.
- Ferguson-DeBose (1977), a pag.100

[…] variation may be part of ongoing language change, i.e., change over time in the conventions of language behaviour in the community.
- Ferguson-DeBose (1977), a pag.101

Variation along all four dimensions may occur in phonology, morphology, semantics, and lexicon, or discourse structure […].
- Ferguson-DeBose (1977), a pag.101