This chapter examines sympathy and antipathy in the ancient Mediterranean and their reception in early modern thought through the framework of occult qualities. It focuses on Galen’s efforts to explain hidden natural powers and how these ideas were later expanded by Jean Fernel in On the Hidden Causes of Things (1548), a key text in pre-Cartesian discourse. Galen integrated earlier Greek medical and philosophical traditions, using sympathy to explain how nature sustains life and structures interactions between natural bodies. While he implicitly linked sympathy with antipathy in On the Natural Faculties, this chapter argues that he avoided direct engagement with antipathy due to its association with amulets and non-Greek, particularly Egyptian, medical practices. This selective treatment left conceptual gaps that Fernel later sought to address. By fully incorporating both sympathy and antipathy, Fernel developed a more systematic account of occult qualities, positioning them as central to natural philosophy and medicine.