An ounce of action is worth a ton of theory.
In theory there is no difference between theory and practice. In practice there is.
The truth of a theory can never be proven, for one never knows if future experience will contradict its conclusions.
The girl I find who wants to talk about quantum theory in a bar is the one I want to marry.
It is a capital mistake to theorize before one has data.
We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct. My own feeling is that it is not crazy enough.
In making theories, always keep a window open so that you can throw one out if necessary.
If the facts don't fit the theory, change the facts.
Read no history: nothing but biography, for that is life without theory.
A young man is a theory, an old man is a fact.
A professor must have a theory as a dog must have fleas.
Theory helps us to bear our ignorance of facts.
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 simple datum of experience.
Some theories are good for nothing except to be argued about.
Socrates thought and so do I that the wisest theory about the gods is no theory at all.
Our theories of the eternal are as valuable as are those which a chick which has not broken its way through its shell might form of the outside world.
It is an acknowledged truth in philosophy that a just theory will always be confirmed by experiment.
Without a revolutionary theory there cannot be a revolutionary movement.
The theory that music has a depraving effect on morals has now been abandoned to the old women of both sexes.
It is amazing how much theory we can do without when work actually begins.
Conjecture as to things useful, is good; but conjecture as to what it would be useless to know, is very idle.
There can be no theory of any account unless it corroborate with the theory of the earth.
I never once made a discovery ... I speak without exaggeration that I have constructed three thousand different theories in connection with the electric light ... Yet in only two cases did my experiments prove the truth of my theory.
A theory in its day helps to solve the problems of the day.
I am not limiting myself to theories, so I never question the rightness to my approach.
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