Mathematics is everywhere and yet its objects are nowhere. There may be five apples on the table but the number five itself is not to be found in, on, beside or anywhere near the apples. So if not in space and time, where are numbers and other mathematical objects such as perfect circles and functions? And how do we humans discover facts about them, be it Pythagoras Theorem or Fermat s Last Theorem? The metaphysical question of what numbers are and the epistemological question of how we know about them are central to the philosophy of mathematics. These and related philosophical questions...