Thomas's commentaries on Aristotle were written around 1266–1272, and his commentary on the Physics was likely written towards the beginning of his second period of teaching in Paris (1268–1269). The work as a whole is a treatment of the science of nature: beginning with the principles of coming to be, Thomas masterfully builds on Aristotle's treatment of matter and form, place and void, motion and time, before finally concluding with the demonstration of the existence of the First Unmoved Mover.