This book deals with epistemic expressions: the linguistic means we have for expressing our degree of certainty about and our type of evidence for propositions about the world. It presents a cross-linguistic study of such expressions and demonstrates that they behave in a way that can be described in terms of a coherent but complex meaning domain. In order to account for this behaviour the book proposes to analyse epistemic meaning in terms of a coherent but complex cognitive structure which is bound up with our cognitive capacity for relating our conception of the world to the world.