As a mathematical discipline travels far from its empirical source... it is beset with very grave dangers. It becomes more and more purely aestheticizing, more and more purely l'art pour l'art. ...In other words, at a great distance from its empirical source, or after much "abstract" inbreeding, a mathematical subject is in danger of degeneration.
From the opening material of the book John von Neumann and Modern Economics. I highly recommend the chapter by Paul Samuelson.
