Existential contextuality and the models of Meyer, Kent, and Clifton

It is shown that the models recently proposed by Meyer, Kent, and Clifton (MKC) exhibit a novel kind of contextuality, which we term existential contextuality. In this phenomenon it is not simply the pre-existing value but the actual existence of an observable which is context dependent. This result confirms the point made elsewhere, that the MKC models do not, as the authors claim, "nullify" the Kochen-Specker theorem. It may also be of some independent interest.