undecidable

:  not capable of being decided :  not decidable … a huge popular audience, most of whom must have been baffled and exasperated by its elaborate and undecidable mystifications. — David Lodge … deconstruction, which teaches that literature is essentially “undecidable,” beyond interpretation … — James Atlas To be complete such a system must be able to prove that any formula expressible in its language (a mathematical equation, for example, or a statement in symbolic logic) is either true or false; nothing can be undecidable. — George Johnson