"Our school, madame, postulates, first of all, that since the
science of mathematics is an abstract science, it is best inculcated by
some concrete example."
Said the Queen, "But that sounds rather complicated."
"It occasionally leads to complications," Jurgen admitted, "through
a choice of the wrong example. But the axiom is no less true."
"Come, then, and sit next to me on this couch if you can find it in
the dark; and do you explain to me what you mean."
"Why, madame, by a concrete example I mean one that is perceptible
to any of the senses -- as to sight or hearing, or touch --"
"Oh, oh!" said the Queen, "now I perceive what you mean by a concrete
example. And grasping this, I can understand that complications must of
course arise from a choice of the wrong example."
- -- James Branch Cabell, "Jurgen"