The ultimate law of language is, dare we say, that nothing can ever reside in a single term. This is a direct consequence of the fact that linguistic signs are unrelated to what they designate and that, therefore, 'a' cannot designate anything without the the aid of 'b' and vice versa, or, in other words, that both have value only by the difference between them.
Ferdinand de SaussureThe critical principle demanded an examination, for instance, of the contribution of different periods, thus to some extent embarking on historical linguistics.
Ferdinand de Saussure