The difference is mostly in degree. We use 'harsh' and 'cruel' to talk mostly about two situations: 1. punishments 2. human interaction For punishments, 'harsh' means that the punishment is pretty severe for the crime. 'Cruel', however, is used for punishments that should NEVER happen to anyone because they are inhumane. For instance, under Hammurabi's Code, a thief would have his hand cut off. That's cruel. For interaction, it usually describes the way people talk to each other or treat each other. If an unattractive person asks you what you think about their appearance, you can respond in many different ways. Harsh: I don't find you attractive at all. That's very honest and blunt, and will probably hurt their feelings. However, it's only harsh because you were so clear. Cruel: Ugly people like you should not be allowed to have children. That's cruel because it is not only unnecessary, it's clearly said to severely hurt the person's feelings in a situation that does not justify that level. 'Cruel' implies that the cruel person is trying to cause as much pain as possible, usually just because they want to.

They are synonyms, however, cruel is a stronger word. Cruel means willfully choosing to cause pain or suffering, while harsh can mean severe or extreme without crossing the line to evil. "The cruel man beat his child with a whip." - (We know the man was choosing to be evil.) "The father was harsh when he disciplined his son." - (The man may have used words or actions that most parents would not take, but we aren't sure how close to evil he was.) These words are very close; the difference between them is very subtle.

They are similar. Someone can behave "harshly" when enforcing a law or principle but without always realising that they are being too strict. "Cruel" is worse than "harsh" because it implies that the person had a bad intention when doing harm to another. A couple of examples: The UN Declaration of Human Rights refers to "cruel and inhuman treatment". People talk about the "harsh reality" of life or some aspect of life.