I look at a disagreement between Elizabeth Anscombe, on the one hand, and Peter Winch and Ilham Dilman, on the other, about whether it is legitimate to call something an error that counts as knowledge within some alien system of belief; and I look also at the question what Wittgenstein's view was. I try to show that our understanding of what is real cannot be adequately elucidated if we consider only its role within language-games, and I argue that an important element in our thinking about what is and is not real emerges in our response to conflicting modes of thought.