Concerning the Nature of Good, Against the Manichæans 4

St Augustine of Hippo (AD 354–430) · De natura boni · PL 42, 551–572

4 Evil is Corruption of Measure, Form, or Order PL 42, 553

When accordingly it is inquired, whence is evil, it must first be inquired, what is evil, which is nothing else than corruption, either of the measure, or the form, or the order, that belong to nature. Nature therefore which has been corrupted, is called evil, for assuredly when incorrupt it is good; but even when corrupt, so far as it is nature it is good, so far as it is corrupted it is evil.

Malum est corruptio modi, speciei aut ordinis. Proinde cum quaeritur unde sit malum, prius quaerendum est quid sit malum: quod nihil aliud est quam corruptio, vel modi, vel speciei, vel ordinis naturalis. Mala itaque natura dicitur, quae corrupta est: nam incorrupta utique bona est. Sed etiam ipsa corrupta, in quantum natura est, bona est; in quantum corrupta est, mala est.

Philip Schaff (ed.), Buffalo/New York: Christian Literature Publishing Co., 1886-1889. Public domain: English translation first published 1885-1900 (Nicene and Post-Nicene Fathers, First Series). Latin: Migne, Patrologia Latina (1844-1855), public domain; transcription from Corpus Corporum (University of Zurich).