The more narrowly we examine language, the sharper becomes the con?ict - tween it and our requirement. (For the crystalline purity of logic was, of course, not a result of investigation; it was a requirement. ) The con?ict becomes intolerable; the requirement is now in danger of becoming empty. We have got onto slippery ice where there is no friction and so in a certain sense the conditions are ideal, but also, just because of that, we are unable to walk. We want to walk; so we need 1 friction. Back to the rough ground! Ludwig Wittgenstein This manuscript consists of four related parts: a brief overview of Wittgensteins p- losophy of language and its relevance to information systems; a detailed explanation of Wittgensteins late philosophy of language and mind; an extended discussion of the re- vance of his philosophy to understanding some of the problems inherent in information systems, especially those systems which rely on retrieval based on some representation of the intellectual content of that information. And, fourthly, a series of detailed footnotes which cite the sources of the numerous quotations and provide some discussion of the related issues that the text inspires. The ?rst three of these parts can each be read by itself with some pro?t, although they are related and do form a conceptual whole.