How did Speusippus change Plato’s mathematical approach to reality?

Speusippus, who succeeded Plato as head of the Academy, shifted the focus of the school by emphasizing the importance of numbers and numerical combinations while deemphasizing the role of Forms.1

While Plato’s metaphysics relied on the postulation of eternal, unchanging Forms, Speusippus organized reality into a hierarchy of increasingly spiritual spheres. He placed the sphere of the soul between the realm of pure numbers—which he termed "mathematicals"—and the realm of the body, or "the sensible".21

Furthermore, Speusippus adopted the doctrine that all reality is derived from two opposite principles: "the One" and "the indeterminate dyad." Unlike his colleagues, who interpreted these principles as representing good and evil, Speusippus explicitly denied that they possessed moral qualities, focusing instead on their role in explaining the presence of unity and multiplicity in the universe.1