Chapter 24: the theme of the harmony of the spheres appears already in Plato and is criticized (as a Pythagorean theory) in Aristotle: if there is such a harmony, why is it that we do not hear it? Despite Aristotle’s criticism, various attempts were made in Antiquity to provide an answer to the question. In Chapter 24 I present an answer to be found in Simplicius which, I argue, goes back to Iamblichus: Pythagoras alone can hear the celestial harmony, whereas we in general cannot; this is because Pythagoras has a faculty corresponding to and able to sense this harmony, an astral vehicle of the soul which is pure, as compared to the impure accretions our souls accumulate in our descent to the body and which prevent us from hearing the celestial music. I describe this music, how Pythagoras educated himself in hearing it and how he composed audible music imaging it for the moral education of his followers.