How we cite our quotes: (Story.Chapter.Paragraph)
Quote #4
[Rincewind] tried to explain that magic had indeed once been wild and lawless, but had been tamed back in the mists of time by the Olden Ones, who had bound it to obey among other things the Law of Conservation of Reality; this demanded that the effort needed to achieve a goal should be the same regardless of the means used. (2.1.7)
All supernatural elements on Discworld have to obey certain laws of nature like the Law of Conservation of Reality. In a way, this makes the supernatural anything but. It's completely natural there; it's just super for us.
Quote #5
As far as [Rincewind] could recall, the tree people had died out centuries before. They had been out-evolved by humans, like most of the other Twilight Peoples. Only elves and trolls had survived the coming of Man to the Discworld; the elves because they were altogether too clever by half, and the trollen folk because they were at least as good as humans at being nasty, spiteful and greedy. (2.5.31)
Even on the Discworld, some things don't change. In the evolution of species, humans still come out on top. And does anyone else think survival of the nastiest sounds way more apt than fittest?
Quote #6
That did not solve the problem of those places on the Disc which, during the wars, had suffered a direct hit by a spell. The magic faded away—slowly, over the millennia, releasing as it decayed myriads of sub-astral particles that severely distorted the reality around it… (3.3.4)
Again, we see idea that the supernatural would have drawbacks comparable to the drawbacks of our reality. In this case, the "sub-astral particles" are suspiciously similar to the problems resulting of nuclear fallout. We wonder what the half-life of a fireball spell is?