According to the principle of bivalence, an utterance that says something is either true or false. The sentence uttered may itself be classified as true or false, relative to the context of utterance (this context relativity will be left tacit). Bivalence is integral to all standard explanations of the formal systems at the core of modern logic. For Frege, Russell and the younger Wittgenstein, a logically perfect language is two-valued. Every wellformed formula in it is true or false.