William Whewell...on mind and matter

...these metaphysical discussions are not to be put in opposition to the study of facts, but are to be stimulated, nourished and directed by a constant recourse to experiment and observation. The cultivation of ideas is to be conducted as having for its object the connexion of facts; never to be pursued as a mere exercise of the subtlety of the mind, striving to build up a world of its own, and neglecting that which exists about us. For although man may in this way please himself, and admire the creations of his own brain, he can never, by this course, hit upon the real scheme of nature. With his ideas unfolded by education, sharpened by controversy, rectified by metaphysics, he may understand the natural world, but he cannot invent it. At every step, he must try the value of the advances he has made in thought by applying his thoughts to things.

- Philosophy of the Inductive Sciences, 1847