This chapter argues that the Epicureans defend a kind of ethical naturalism. The first section of the chapter, focusing on ontology, shows that for the Epicureans justice is conceived of as an accidental property (sumptōma/eventum) and is of the same general sort as the properties that are investigated in science. The second section, turning to moral epistemology, argues that, on the Epicurean view, what is just is directly perceived, showing that the investigation of ethical properties happens in the same general way as investigation in the sciences on the Epicurean view.