The chapter gives an account Epicurus’ natural philosophy and his attitude to the sciences. Epicurus’ mission was to liberate people from the fear of death and the gods, and science was subordinate to that project, practiced to show that nature acts without divine intervention. He was skeptical about mathematics, due to his commitment to atomism, and about astronomy, because knowledge should be based on clear foundations unavailable for deciding issues such as the planets’ sizes. Sensation dictates there are two constituents of reality: bodies, directly attested by sense perception; and the void, the space where bodies exist and move. Infinite atoms move through space, forming countless worlds (kosmoi), which at some point will again fall apart into their constituent atoms. Epicurus considers naturalistic explanations of phenomena to show they are not divine. But his philosophy of nature insists upon natural causes (as opposed to geometrical models), is consistently materialist and mechanistic, and is thus anti-teleological.
The chapter discusses the natural philosophy of the ancient Stoics including the attitude they took towards the so-called special and applied sciences (technai). After a historical outline introducing the main facts and personalities (sec. 1), the role and status of natural philosophy within the Stoic system are explained, with special reference to the moral and theological dimension of the study of nature, that is, the Stoic view of the world as a rationally structured and providentially determined whole and what this view implies for our way of living (sec. 2). Two subsequent sections are concerned with Stoic materialist physics on both the universal (macrocosmic) and the individual (microcosmic) level respectively (sec. 3 and sec. 4). The next section is specifically devoted to exploring Stoic views on, and involvement with, applied sciences and arts such as astronomy, mathematics and medicine (sec. 5). The Epilogue sums up the main results from the preceding discussion (sec. 6).