The author assumes that there are two fundamentally different theoretical and methodological views in the tradition of linguistics: determinism and indeterminism. The first direction is based on the algorithmic, systemic, and computational approach, while the second on the empiriocentric, experiential, phenomenological approach. Although scientific formations founded on the first or second theoretical assumption are polarized, in fact, both approaches represent an ambivalent nature of language and its characteristics which complement each other in a linguistic activity. The need to use indeterminism methodology in linguistic research results from the fact that language constructions in practice are modified under the influence of factors that are extralinguistic in nature – primarily under the influence of human experience. Therefore, the author considers the phenomenon of approximation as a basic principle of language activity which determines various types of modifications of language rules in the field of grammar. Using the example of the category of voice, the author shows that due to approximation, the oppositions of functional classes of an active and passive voice, existing in the language system, are blurred.