We must avoid here two complementary errors: on the one hand that the world has a unique, intrinsic, pre-existing structure awaiting our grasp; and on the other hand that the world is in utter chaos. The first error is that of the student who marvelled at how the astronomers could find out the true names of distant constellations. The second error is that of the Lewis Carroll's Walrus who grouped shoes with ships and sealing wax, and cabbages with kings...