Oh, my dear Vimes, history changes all the time. It is constantly being re-examined and re-evaluated, otherwise how would we be able to keep historians occupied? We can't possibly allow people with their sort of minds to walk around with time on their hands.

If the government ever imposes a tax on books - and I wouldn't put it past them - I'm in dead trouble.

Any wizard bright enough to survive for five minutes was also bright enough to realize that if there was any power in demonology, then it lay with the demons. Using it for your own purposes would be like trying to beat mice to death with a rattlesnake.

The most prudent thing any intelligent animal can do, if it would prefer its descendents not to spend a lot of time on a slab with electrodes clamped to their brains or sticking mines on the bottom of ships, or being patronised by zoologists, is to make bloody certain humans don't find out about it.

If you really want to upset a witch, do her a favor which she has no means of repaying. The unfulfilled obligation will nag at her like a hangnail.

That was always the dream, wasn't it? 'I wish I'd known then what I know now'? But when you got older you found out that you NOW wasn't YOU then. You then was a twerp. You then was what you had to be to start out on the rocky road of becoming you now, and one of the rocky patches on that road was being a twerp.

There is no doubt that being human is incredibly difficult and cannot be mastered in one lifetime.