In theory, theory and practice are the same. In practice, they are not.

The satisfaction of physical needs is indeed the indispensable pre-condition of a satisfactory existence, but in itself it is not enough. In order to be content, men must also have the possibility of developing their intellectual and artistic powers to whatever extent accords with their personal characteristics and abilities.

Human beings can attain a worthy and harmonious life only if they are able to rid themselves, within the limits of human nature, of the striving for the wish fulfillment of material kinds. The goal is to raise the spiritual values of society.

Life is like riding a bicycle. If you want to stay balanced you've got to keep moving forward.

Logic will get you from A to B. Imagination will take you everywhere.

On the left-hand side of the field equation we may add the fundamental tensor guv, multiplied by a universal constant, -λ, at present unknown, without destroying the general covariance.

Nothing causes more consternation in a group of hypocrits than one honest man.