 In [Letters] sections 11–18 al-Fārābī undertakes to identify several arts or sciences in these terms, namely “the art of logic and the sciences of nature, politics, mathematics and metaphysics”. The first step is to identify their subjects. In all these cases, he says, the “primary subjects” are the primary concepts ([Letters] 66.20f). For example, in mathematics we study primary concepts from the point of view of quantity, abstracting from their other features ([Letters] (15) 67.19–68.5). (See Druart 2007 and Menn 2008 on the important question of how metaphysics fits into this picture.)