The existence of fluctuations in forms means that certain structures are winning out over others, for alternative forms never stay in equilibrium for long.
- Nida (1949), a pag.3

Our descriptions of languages tend to give the impression that they are static, fixed structures. This is, of course, the attitude of the average speaker of a language, and yet we do realize that there are (1) fluctuations of forms, e.g. 'roofs' vs. 'rooves', 'hoofs' vs. 'hooves', 'proven' vs. 'proved', and 'dove' vs. 'dived' [...]
- Nida (1949), a pag.3