Full Idea
Logic (like geometry and arithmetic) applies only to fictitious entities that we have created.
Gist of Idea
Logic and maths refer to fictitious entities which we have created
Source
Friedrich Nietzsche (The Will to Power (notebooks) [1888], §516)
Book Reference
Nietzsche,Friedrich: 'The Will to Power', ed/tr. Kaufmann,W /Hollingdate,R [Vintage 1968], p.280
A Reaction
This finds Nietzsche on the relativist wing of logical empiricism. The thing is, fictitious entities can have a close relationship with truth, as in a great novel. I believe in necessary logical truth, but there are many ways of slicing it.