On The Substance Of Evil is a philosophical treatise written by Proclus, a prominent Neoplatonist philosopher of the 5th century AD. The book explores the nature and origins of evil, as well as its relationship to the divine and the human psyche. Proclus argues that evil is not a positive substance, but rather a lack or absence of goodness. He also discusses the role of free will in the existence of evil, and how it relates to the concept of moral...