Many philosophers are attracted by the robust insistence that these beliefs need no defence, but also have a strong sense that Moore missed an important point. One reaction, associated with Stroud, is that although my certainty that I have two hands needs no defence in our everyday practices, the same is not the case when we attempt a distinctively philosophical assessment of our position. If we are to resist the suggestion that sceptical challenges are relevant to the evaluation of our beliefs, the attractive element of the view needs a more sophisticated formulation than it received from Moore. An influential argument that standard sceptical possibilities are irrelevant to our practice of epistemic evaluation was contained in Robert Nozick's Philosophical Explanations . Since, if I had been a brain in a vat, I would still have believed that I was not one, I do not know that I am not a brain in a vat.
Sceptical challenges are thus of no epistemological importance.
Even if one of my beliefs tracks the truth, I may be in no position to tell whether it is. Since Logical Positivists attempted to deny the meaningfulness of dream or demon possibilities on the grounds that we do not know what experience would be relevant to assessing their truth-value, philosophers have appealed to the theory of meaning. It is part of Donald Davidson's theory of interpretation that, when we assign meanings to someone's utterances or contents to their beliefs, we are guided by a demand that we make their beliefs largely truthful and their inferences largely sound. If we encountered a brain in a vat, then, if we ascribed beliefs to it at all, they would be predominantly true beliefs about the 'world' created by the computer rather than predominantly false beliefs about our familiar external world. Whether or not we can conceive of the possibility that we are the victims of demons or wicked scientists, we can make no sense of our claims being both meaningful and substantially false.