We know a lot of things ? or, at least, we think we do. Epistemology is the branch of philosophy that studies knowledge: its main features, the dynamics of its growth, as well as its claims for truth, validity, and progress. In this course ? which is designed as a series of seminars held by the students, preceded by a few introductory lectures ? we will consider some of the key contributions to the philosophical debate about the growth of scientific knowledge in the twentieth century, from Logical Positivism to Karl Popper, from Thomas Kuhn to Paul Feyerabend.