Full Idea
We have fixed up a world for ourselves in which we can live, with bodies, lines, planes, causes, motion and form; without these articles of faith nobody would endure life. But that does not mean they have been proved. Life is no argument.
Gist of Idea
We assume causes, geometry, motion, bodies etc to live, but they haven't been proved
Source
Friedrich Nietzsche (The Gay (Joyful) Science [1882], §121)
Book Reference
Nietzsche,Friedrich: 'The Gay Science', ed/tr. Kaufmann,Walter [Vintage 1974], p.177
A Reaction
It is hard to disagree. A lot of recent thought suggests that they are Hume's 'natural beliefs', like truth and induction, which simply can't be proved. 'Unprovable' does not mean 'incorrect', however.