 In the Introduction to Arithmetic, Nicomachus assigns to Pythagoras the Platonic division between the intelligible and sensible world, quoting the Timaeus as if it were a Pythagorean text (I 2). He also assigns Aristotelian ideas to Pythagoras, in particular a doctrine of immaterial attributes with similarities to the Aristotelian categories (I 1). Nicomachus divides reality into two forms, magnitude and multitude. Wisdom is then knowledge of these two forms, which are studied by the four sciences, which will later be known as the quadrivium: arithmetic, music, geometry and astronomy. He quotes a genuine fragment of Archytas (Fr. 1) in support of the special position of these four sciences. Nicomachus presents arithmetic as the most important of the four, because it existed in the mind of the creating god (the demiurge) as the plan which he followed in ordering the cosmos (I 4), so that numbers thus appear to have replaced the Platonic forms as the model of creation (on forms and numbers in Nicomachus see Helmig 2007). It is striking that, along with this Platonization of Pythagoreanism, Nicomachus does give an accurate presentation of Philolaus’ basic metaphysical principles, limiters and unlimiteds, before attempting to equate them with the Platonic monad and dyad (II 18).