"The system becomes more coherent as it is further extended. The elements which we require for explaining a new class of facts are already contained in our system. In false theories, the contrary is the case."

"Fundamental ideas are not a consequence of experience, but a result of the particular constitution and activity of the mind, which is independent of all experience in its origin, though constantly combined with experience in its exercise."

"We cannot observe external things without some degree of Thought; nor can we reflect upon our Thoughts, without being influenced in the course of our reflection by the Things which we have observed."

"Hence no force, however great, can stretch a cord, however fine, into a horizontal line which is accurately straight: there will always be a bending downwards."

"Every failure is a step to success."

"It is a test of true theories not only to account for but to predict phenomena."