A linguistic theory which searches for the specific structure of language through an exclusively formal system of premisses must, while continually taking account of the fluctuations and changes of speech, necessarily refuse to grant exclusive significance to those changes; it must seek a ‘constancy’, which is not anchored in some “reality” outside language – a constancy that makes a language a language, whatever language it may be, and that makes a particular language identical with itself in all its various manifestations.
- Hjelmslev (1961), a pag.8