Playfullness is the essential feature of productive thought.

Although words exist for the most part for the transmission of ideas, there are some which produce such violent disturbance in our feelings that the role they play in the transmission of ideas is lost in the background.

Education is only a ladder to gather fruit from the tree of knowledge, not the fruit itself

The indifference, callousness and contempt that so many people exhibit toward animals is evil first because it results in great suffering in animals, and second because it results in an incalculably great impoverishment of the human spirit.

Everything that exists in your life, does so because of two things: something you did or something you didn't do.

Physics is an attempt conceptually to grasp reality as something that is considered to be independent of its being observed. In this sense one speaks of physical reality.

The opinion prevailed among advanced minds that it was time that belief should be replaced increasingly by knowledge; belief that did not itself rest on knowledge was superstition, and as such had to be opposed.