Philolaus (470?–390? B.C.), pre-Socratic Greek philosopher from Croton in southern Italy, the first Pythagorean to write a book. The surviving fragments of it are the earliest primary texts for Pythagoreanism, but numerous spurious fragments have also been preserved. Philolaus’s book begins with a cosmogony and includes astronomical, medical, and psychological doctrines. His major innovation was to argue that the cosmos and everything in it is a combination not just of unlimiteds (what is structured and ordered, e.g. material elements) but also of limiters (structural and ordering elements, e.g. shapes). These elements are held together in a harmonia (fitting together), which comes to be in accord with perspicuous mathematical relationships, such as the whole number ratios that correspond to the harmonic intervals (e.g. octave % 1 : 2). He argued that secure knowledge is possible insofar as we grasp the number in accordance with which things are put together. His astronomical system is famous as the first to make the earth a planet. Along with the sun, moon, fixed stars, five planets, and counter-earth (thus making the perfect number ten), the earth circles the central fire (a combination of the limiter ‘center’ and the unlimited ‘fire’). Philolaus’s influence is seen in Plato’s Philebus; he is the primary source for Aristotle’s account of Pythagoreanism.
See also PYTHAGORA. C.A.H.