Proclus' On the Existence of Evils is not a commentary, but helps to compensate for the dearth of Neoplatonist ethical commentaries. The central question addressed in the work is: "How can there be evil in a providential world?" Neoplatonists agree that evil cannot be caused by higher and worthier beings. Plotinus had said that evil is matter. Unlike Aristotle, he collapsed evil into mere privation or lack, thus reducing its reality. He also protected higher causes from responsibility for evil by saying that evil may result from a combination of goods. Proclus objects: evil is real, and not the mere privation of form. Evil, in his formulation, is a parasite that feeds upon good. Higher beings are thus vindicated: they are the causes only of the good upon which evil feeds.
Proclus Lycaeus (/ˈprɒkləs ˌlaɪˈsiːəs/; 8 February 412 – 17 April 485 AD), called the Successor (Greek Πρόκλος ὁ Διάδοχος, Próklos ho Diádokhos), was a Greek Neoplatonist philosopher, one of the last major Classical philosophers (see Damascius). He set forth one of the most elaborate and fully developed systems of Neoplatonism. He stands near the end of the classical development of philosophy, and was very influential on Western medieval philosophy (Greek and Latin).