Theories of justice, for example, may be radically different. Perhaps people are talking at cross-purposes — they simply are employing different concepts, and the theories they offer may be equally adequate (or inadequate) as accounts of the things they have in mind. Or perhaps there is real disagreement: they are offering competing accounts of the nature of justice. They are both discussing the same subject matter.
Across time our ideas change enormously: our idea of the gene is very different form what it once was, for example. Is it a change of subject matter, a change of opinion, or is there no fact of the matter?
This is a course about the nature of concepts and conceptual change. We will start with an examination of some of the existing philosophical and psychological literature about the nature of concepts. We will then examine the various roles that a theory of concepts might be expected to play. We then identify one of those roles, and explore a variant of two-dimensional semantics as a promising candidate to play that role. It will both give an account of what concepts are, and of how it is possible to settle whether in cases of significant change or disagreement on a topic whether the arguments are at cross purposes. We may also deal with hyperintentionally distinct concepts.