The problem medieval writers faced
If God is entirely good and all-powerful, why is there pain, cruelty and death? Later philosophers called this the problem of evil. Medieval thinkers did not use that label, but they worked on it constantly. The question mattered for practical reasons too: preachers, confessors and ordinary families had to make sense of plague, war, famine and personal loss.
This article gives an overview of the main answers and marks where thinkers disagreed. It does not cover the details of particular sins, which belong to the discussion of medieval sin.
Evil as a lack of good
The most influential answer in Western Christianity came from Augustine of Hippo. In his view, everything that exists is good in so far as it exists, because God made it. Evil is therefore not a substance or a rival thing; it is a lack, a corruption or a falling short of the good that something ought to have. Blindness is not a thing in itself, but the absence of sight in an eye that should see.
Medieval writers repeated this idea for centuries. It had two attractions. It protected the belief that God created only good things, and it explained why evil always seems to feed on something else, since a corruption needs something to corrupt. Critics, then and now, have asked whether calling evil an absence really makes pain feel any less real. Most medieval writers did not think it did; they simply claimed it explained where evil came from.
Free will and moral evil
A second answer concerned moral evil, meaning wrongs people choose to do. The usual explanation was that God gave angels and humans free will, because love and virtue that are forced would not be real virtue. Free beings can misuse their freedom. On this account, the first sin of the rebel angels and then of Adam and Eve introduced disorder into creation, and human wrongdoing followed from a will turned toward lesser goods.
This answer left a harder question: why would God create beings who might fall? Writers such as Anselm of Canterbury, around 1100, and later Thomas Aquinas, argued that a world containing free creatures who could freely return to God was a greater good than a world without them. They also admitted that the full reasons lay beyond human understanding.
Natural suffering and the larger order
What about suffering that nobody chooses, such as disease or storms? Here medieval thinkers often appealed to order. A common argument held that the universe is more beautiful and complete for having many kinds of things in it, and that individual losses can look different from the viewpoint of the whole. The late Roman writer Boethius, whose Consolation of Philosophy was widely read throughout the Middle Ages, made a version of this argument and tied it to divine providence.
Another widespread idea was that suffering could be educational or purifying, a form of discipline that might lead the sufferer toward repentance or patience. That is one reason the experience of pain is linked in sermons to penance and, after death, to the doctrine of purgatory. Modern readers sometimes find this explanation hard, and some medieval writers shared the unease; the Book of Job was constantly read because it refuses easy answers.
Rival views: dualism
Not everyone accepted that evil was a lack. Dualist traditions, in which good and evil are two opposing principles, had a long history. The late antique Manichaeans taught this, and Augustine himself had been attracted to them before rejecting their view. In the central and later Middle Ages, groups often called Cathars, in parts of southern France and northern Italy, were accused of dualist beliefs, such as holding that the material world was the work of an evil power.
Historians debate how coherent and widespread these beliefs were, partly because much of what we know comes from hostile sources written by opponents. What is clear is that the Church saw dualism as a serious threat, and that responses to it included preaching campaigns, and later, heresy trials. Mainstream theologians sharpened their insistence that creation was good.
Where the disputes lay
Several questions stayed open:
- Why did God permit evil at all? Answers varied, and many writers fell back on mystery.
- Could God have made a world without evil? Some argued yes but that this world was better; others warned that asking such questions risked limiting God.
- How much could reason establish? Thinkers disagreed about the balance between faith and reason in handling questions like this.
- How far was moral evil the result of ignorance rather than malice? Intellectualist and voluntarist approaches differed on whether bad choices came mainly from misjudging the good or from a misdirected will.
Good and evil in ordinary life
For most people the debate came through simple images. Sermons, stories and religious iconography showed devils, angels and the weighing of souls at the Last Judgment, turning a hard argument into a vivid moral contest. The sense that daily choices lined up on one side or the other helps explain the popularity of lists of virtues and vices. At the same time, medieval moral teaching was full of gray areas, as the careful distinctions of confessors show.
A note on certainty
Because theological writing was produced by a small educated group, we know the learned debate better than popular belief. What we can say is that the dominant Western answer treated evil as a corruption of something good, explained moral evil through free will, and left the deepest questions acknowledged as mysteries.