You know how it always is, every new idea, it takes a generation or two until it becomes obvious that there's no real problem. I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem.

-Feynman, Richard P(hillips)
  Explaining his feelings on quantum mechanics. In the International Journal of  Theoretical Physics, vol.21.

It is hard for a woman to define her feelings in language which is chiefly made by men to express theirs.

-Hardy,Thomas
  Far from the Madding Crowd, ch.81.

We ought to define a man's income as the maximum value which he can consume during a week, and still expect to be as well off at the end of the week as he was at the beginning.

-Hicks, SirJohn Richard
  Value and Capital (2nd edn).

Nobody has ever been able to define jazz satisfactorily. This is probably because anyone who was capable of doing so never really wantedto, knowing how muchyou would have to leave out of the definition.

-Kingsley, Mary Henrietta
  The Jazz  Anthology, ch.1

To define an expression is, paradoxically speaking, to explain how to get along without it. To define is to eliminate.

-Quine,Willard Van Orman
  Quiddities,'Definition'.