Human life is driven forward by its dim apprehension of notions too general for its existing language.

Knowledge keeps no better than fish.

Nature is probably quite indifferent to the aesthetic preferences of mathematicians.

There are two principles inherent in the very nature of things, recurring in some particular embodiments whatever field we explore - the spirit of change, and the spirit of conservation. There can be nothing real without both. Mere change without conservation is a passage from nothing to nothing. . . . Mere conservation without change cannot conserve. For after all, there is a flux of circumstance, and the freshness of being evaporates under mere repetition.

Every intellectual revolution which has ever stirred humanity into greatness has been a passionate protest against inert ideas. Then, alas, with pathetic ignorance of human psychology, it has proceeded by some educational scheme to bind humanity afresh with inert ideas of its own fashioning.

Without adventure civilization is in full decay.

To see what is general in what is particular, and what is permanent in what is transitory, is the aim of scientific thought.