I am coming more and more to the conviction that the necessity of our geometry cannot be demonstrated, at least neither by, nor for, the human intellect...geometry should be ranked, not with arithmetic, which is purely aprioristic, but with mechanics.
Gauss, Karl Friedrich (1777-1855)
Quoted in J. Koenderink Solid Shape, Cambridge Mass.: MIT Press, 1990.
Found at Furman University's Mathematical Quotation Server