What Philosophy is about. Ontology, Philosophy of Knowledge and Ethics. Historical matters. Philosophy of Science or Epistemology? (a question). Formation of Modern Science. Descartes, John Locke, Berkeley, Hume, Kant. The nature of scientific practice, the case of Mathematics and Physics. Empiricism, Logical Positivism and the critique of Popper. Russell and Wittgenstein about the foundations of Mathematics. The concept of Mathematical Practice and Modes of Existence of mathematical “objects”. Semantics and interpretive models.