 Recall that in the Enumeration of the Sciences Fârâbî describes metaphysics as investigating three things—being and its attributes, the principles of the particular sciences, and separate incorporeal beings (especially God)—but he does not explain why the three investigations fall under a single science or what premisses the science can draw on to resolve the questions. In On the Aims of the Metaphysics he tries to explain how these investigations fit together. The science starts by studying its primary subject, namely being and unity; then, “since the science of opposites is the same”, their opposites, non-being and multiplicity; then it divides being and unity and their opposites into their main species, or rather quasi-species—“quasi” because substances, qualities, and the other categories are each called “being” in a different sense, whereas if being were a genus and they were its species it would be said of them all in the same  sense.[12]  Then the science investigates the attributes and principles of being and unity and their opposites,