I'm on the road, so here are two (dueling?) quotes to make up for the hit-or-miss blogging:

 God forbid that we should give out a dream of our own imagination for a pattern of the world.
- Francis Bacon, Novum Organum, p. 30

It is surprising that people do not believe that there is imagination in  science. It is a very interesting kind of imagination, unlike that of the artist. The great difficulty is in trying to imagine something that you have never seen, that is consistent in every detail with what has already been seen, and that is different from what has been thought of; furthermore, it must be definite and not a vague proposition. That is indeed difficult.  

- Richard Feynman, The Meaning of it All