The truth of a theory can never be proven, for one never knows if future experience will contradict its conclusions.
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.
I cannot seriously believe in it [quantum theory] because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance [spukhafte Fernwirkungen].
I can't stand theory because it is imposed by the intellectual. And the intellectual is, by definition, not a creative person. The intellectual is a person who talks about the creative process, but often doesn't understand it.
It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.
You know it's very hard to maintain a theory in the face of life that comes crashing about you.
The world can doubtless never be well known by theory: practice is absolutely necessary; but surely it is of great use to a young man, before he sets out for that country, full of mazes, windings, and turnings, to have at least a general map of it, made by some experienced traveler.
The Theory of Groups is a branch of mathematics in which one does something to something and then compares the result with the result obtained from doing the same thing to something else, or something else to the same thing.
It is an acknowledged truth in philosophy that a just theory will always be confirmed by experiment.
Theory has nothing to do with a work of art. Pictures which are interpretable, and which contain a meaning, are bad pictures. A picture presents itself as the Unmanageable, the Illogical, the Meaningless.
To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.
Even for practical purposes theory generally turns out the most important thing in the end.
Do not put too much confidence in experimental results until they have been confirmed by theory.
Never fall in love with an idea. They're whores: if the one you're with isn't doing the job, there's always, always, always another.
Imagination is more important than knowledge.
All theory, my friend, is grey, But green is life's glad golden tree.
Make everything as simple as possible, but not simpler.
In theory, practice and theory are the same, but in practice they are different.
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.
I've got a theory that if you give 100% all of the time, somehow things will work out in the end.
Creationists make it sound as though a 'theory' is something you dreamt up after being drunk all night.
If facts conflict with a theory, either the theory must be changed or the facts.
Facts quite often, I fear to confess, like lawyers, put me to sleep at noon. Not theories, however. Theories are invigorating and tonic. Give me an ounce of fact and I will produce you a ton of theory by tea this afternoon. That is, after all, my job.
Your theory is crazy, but it's not crazy enough to be true.
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