Chapter 6 examines Plato’s introduction of mathematical structures in order to explain the natural world. It contrasts his ‘mathematical approach’ to nature with that of the Pythagoreans, and shows how his use of mathematics enables Plato to make motion intelligible in itself to a certain degree. For this, the idea of measuring motion in temporal terms is crucial. However, Plato’s treatment of measurement in the Timaeus does not include measuring the distance covered by a motion. And Plato’s treatment of time and space (the receptacle) as entities of fundamentally different status, taking time to be intelligible in a way in which space is not, prevents him from connecting time and space in an account of speed. It is shown that Plato instead reduces speed to the time a motion takes. The chapter finishes by spelling out the problematic consequences of this reduction – that it only allows for restricted comparability of different motions and that in certain cases it can lead into inconsistencies.