The dissertation is an exploration of the possibility and nature of interpretation. Its thesis is that coming to know what someone believes or desires, or what their words mean, or what they are doing, is not to be distinguished from coming to know something about the world. This thesis is defended, on the one hand, by distancing it from empiricist readings, and, on the other hand, by arguing against idealist or realtivist reasons for rejecting it. ;The dissertation is in two (...) parts. Part I, "Philosophy of Mind," takes up the question whether the thesis stated above implies that agents are mere objects and knowledge of minds is just knowledge of brains. There is, it is true, a sense in which explanations of events under physical descriptions are better as explanations than are explanations of the same events under psychological descriptions; nonetheless, it is argued, psychological descriptions and explanations are neither reducible to nor eliminable in favour of purely physicalistic ones. Part I established that coming to know what someone believes or means is coming to know something about the world--something about the world, that is, under a psychological description. ;Part II, "Philosophy of Language," takes up the question whether there is some difference in kind between knowledge of things conceived as psychological or meaningful and knowledge of things conceived as physical, a difference in addition to that of subject matter. It emerged in Part I that the notion of rationality is central to psychological description and explanation, whereas it plays no role in physical description: is this a difference that makes a difference? It is concluded that interpretation is possible not because speaker and interpreter share a tradition, or a conceptual scheme, or countless basic beliefs, or even because most of their beliefs are true. Rather, the possibility of interpretive knowledge rests on nothing more than that interpreter and speaker are in causal contact with a common environment. Thus in no important respect is interpretive understanding unlike knowledge of physical things. (shrink)