In the previous chapter I had occasion to deal with a challenge to common sense metaphysical realism from a version of neo-Kantian constructivism. I now want to examine another threat to common sense stemming from another quarter, in this case the philosophy of language. I want to discuss an argument put forward by Michael Dummett, an argument which, if sound, would have quite radical implications. Dummett's manifestation argument takes the form of a reductio and has for a striking conclusion the denial of the principle of bivalence, that is, the claim that each and every well-formed statement is either true or false.