Identity and Discrimination, originally published in 1990 and the first book by respected philosopher Timothy Williamson, is now reissued and updated with the inclusion of significant new material. Williamson here proposes an original and rigorous theory linking identity, a relation central to metaphysics, and indiscriminability, a relation central to epistemology. * Updated and reissued edition of Williamson's first publication, with the inclusion of significant new material * Argues for an original cognitive account of the relation between identity and discrimination that has been influential in the philosophy of perception * Pioneers the use of epistemic logic to solve puzzles about indiscriminability * Develops the application of techniques from mathematical logic to understand issues about identity over time and across possible worlds