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

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.

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.

Such simple instincts as bees making a beehive could be sufficient to overthrow my whole theory.

The dimmed outlines of phenomenal things all merge into one another unless we put on the focusing-glass of theory, and screw it up sometimes to one pitch of definition and sometimes to another, so as to see down into different depths through the great millstone of the world.