Valentine: The unpredictable and the predetermined unfold together to make everything the way it is. [...] We're better at predicting events at the edge of the galaxy or inside the nucleus of an atom than whether it'll rain on auntie's garden party three Sundays from now. Because the problem turns out to be different. We can't even predict the next drip from a dripping tap when it gets irregular. Each drip sets up the conditions for the next, the smallest variation blows prediction apart, and the weather is unpredictable in the same way, will always be unpredictable. (1.4)
Chloë: The future is all programmed like a computer – that's a proper theory, isn't it? [...] But it doesn't work, does it?
Valentine: No. It turns out the maths is different.
Chloë: No, it's all because of sex.
Chloë: That's what I think. The universe is deterministic all right, just like Newton said, I mean it's trying to be, but the only thing going wrong is people fancying people who aren't supposed to be in that part of the plan.
Valentine: Ah. The attraction that Newton left out. (2.7)
Augustus: You are not my tutor, sir. I am visiting your lesson by my free will.
Septimus: If you are so determined, my lord. (2.7)