Practical wisdom is only to be learned in the school of experience. Precepts and instruction are useful so far as they go, but, without the discipline of real life, they remain of the nature of theory only. (Quote by - Samuel Smiles)

There can be no theory of any account unless it corroborate with the theory of the earth. (Quote by - Walt Whitman)

There could be no fairer destiny for any physical theory than that it should point the way to a more comprehensive theory in which it lives on as a limiting case. (Quote by - Albert Einstein)

Normal science does not aim at novelties of fact or theory and, when successful, finds none. (Quote by - Thomas Kuhn)

Today, the theory of evolution is an accepted fact for everyone but a fundamentalist minority, whose objections are based not on reasoning but on doctrinaire adherence to religious principles. (Quote by - James D. Watson)

The struggle for existence holds as much in the intellectual as in the physical world. A theory is a species of thinking, and its right to exist is coextensive with its power of resisting extinction by its rivals. (Quote by - Thomas Huxley)

Psychotherapy theory turns it all on you: you are the one who is wrong. If a kid is having trouble or is discouraged, the problem is not just inside the kid; it's also in the system, the society. (Quote by - James Hillman)

No theory is good unless it permits, not rest, but the greatest work. No theory is good except on condition that one use it to go on beyond. (Quote by - Andre Gide)

Quantum theory also tells us that the world is not simply objective; somehow it's something more subtle than that. In some sense it is veiled from us, but it has a structure that we can understand. (Quote by - John Polkinghorne)

Freud was a hero. He descended to the Underworld and met there stark terrors. He carried with him his theory as a Medusa's head which turned these terrors to stone. (Quote by - R. D. Laing)

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

An ounce of action is worth a ton of theory. (Quote by - Ralph Waldo Emerson)

In theory there is a possibility of perfect happiness: To believe in the indestructible element within one, and not to strive towards it. (Quote by - Franz Kafka)

My theory is to enjoy life, but the practice is against it. (Quote by - Charles Lamb)

I'm a games and theory kind of guy. I love puzzles, so it was fun dissecting Shakespeare's prose. (Quote by - Neil Patrick Harris)

I have a theory that the truth is never told during the nine-to-five hours. (Quote by - Hunter S. Thompson)

In order to govern, the question is not to follow out a more or less valid theory but to build with whatever materials are at hand. The inevitable must be accepted and turned to advantage. (Quote by - Napoleon Bonaparte)

I have a theory that the only original things we ever do are mistakes. (Quote by - Billy Joel)

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. (Quote by - Marcel Proust)

Without a revolutionary theory there cannot be a revolutionary movement. (Quote by - Vladimir Lenin)

Theory is splendid but until put into practice, it is valueless. (Quote by - James Cash Penney)

In theory there is no difference between theory and practice. In practice there is. (Quote by - Yogi Berra)

Good art theory must smell of the studio, although its language should differ from the household talk of painters and sculptors. (Quote by - Rudolf Arnheim)

If you want to know the taste of a pear, you must change the pear by eating it yourself. If you want to know the theory and methods of revolution, you must take part in revolution. All genuine knowledge originates in direct experience. (Quote by - Mao Zedong)

If the facts don't fit the theory, change the facts. (Quote by - Albert Einstein)