The theory of evolution by cumulative natural selection is the only theory we know of that is in principle capable of explaining the existence of organized complexity.
Richard Dawkins

Today the theory of evolution is about as much open to doubt as the theory that the earth goes round the sun.
Richard Dawkins

Even for practical purposes theory generally turns out the most important thing in the end.
Oliver Wendell Holmes

All theory, dear friend, is gray, but the golden tree of life springs ever green.
Johann Wolfgang von Goethe

I cannot help fearing that men may reach a point where they look on every new theory as a danger, every innovation as a toilsome trouble, every social advance as a first step toward revolution, and that they may absolutely refuse to move at all.
Alexis de Tocqueville

I have a theory that the best ads come from personal experience. Some of the good ones I have done have really come out of the real experience of my life, and somehow this has come over as true and valid and persuasive.
David Ogilvy

Experience without theory is blind, but theory without experience is mere intellectual play.
Immanuel Kant

Without revolutionary theory there can be no revolutionary movement.
Vladimir Lenin

Without a revolutionary theory there cannot be a revolutionary movement.
Vladimir Lenin

I never had a policy about marriage. I got married very young in life and I always think in all relationships, I've always thought that it's counterproductive to have a theory on that.
Jack Nicholson

Thought and theory must precede all salutary action; yet action is nobler in itself than either thought or theory.
Virginia Woolf

In theory one is aware that the earth revolves, but in practice one does not perceive it, the ground upon which one treads seems not to move, and one can live undisturbed. So it is with Time in one's life.
Marcel Proust

If the Confederacy fails, there should be written on its tombstone: Died of a Theory.
Jefferson Davis

Never worry about theory as long as the machinery does what it's supposed to do.
Robert A. Heinlein

Europe is so well gardened that it resembles a work of art, a scientific theory, a neat metaphysical system. Man has re-created Europe in his own image.
Aldous Huxley

Democracy is beautiful in theory; in practice it is a fallacy.
Benito Mussolini

Let your religion be less of a theory and more of a love affair.
Gilbert K. Chesterton

Democracy is the theory that the common people know what they want, and deserve to get it good and hard.
H. L. Mencken

We must respect the other fellow's religion, but only in the sense and to the extent that we respect his theory that his wife is beautiful and his children smart.
H. L. Mencken

The theory seems to be that as long as a man is a failure he is one of God's children, but that as soon as he succeeds he is taken over by the Devil.
H. L. Mencken