All That Is Not Thought Is Pure

I Entered An Omnibus To Go To Some Place Or Other. At That Moment When I Put My Foot On The Step The Idea Came To Me, Without Anything In My Former Thoughts Seeming To Have Paved The Way For It, That The Transformations I Had Used To Define The Fuchsian Functions Were Identical With Non-euclidean Geometry.

What Is A Good Definition? For The Philosopher Or The Scientist, It Is A Definition Which Applies To All The Objects To Be Defined, And Applies Only To Them; It Is That Which Satisfies The Rules Of Logic. But In Education It Is Not That; It Is One That Can Be Understood By The Pupils.

It Is Far Better To Foresee Even Without Certainty Than Not To Foresee At All.

The Mind Uses Its Faculty For Creativity Only When Experience Forces It To Do So.

One Does Not Ask Whether A Scientific Theory Is True, But Only Whether It Is Convenient.