To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science.

Politics is for the present, but an equation is for eternity.

It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience.

A theory is the more impressive the greater the simplicity of its premises, the more different things it relates, and the more extended its area of applicability.

The theory I propose may therefore be called a theory of the Electromagnetic Field because it has to do with the space in the neighbourhood of the electric or magnetic bodies, and it may be called a Dynamical Theory, because it assumes that in the space there is matter in motion.

The supreme misfortune is when theory outstrips performance.