Because practice is subjective, theory which is always the theory of an object, can't access to the reality of this practice, what it is in itself, but only represent it, in such a way that this representation lets out of itself the real being of practice, the effectivity of the doing. Theory does nothing.

In conclusion, a word about your tired expression that there is a difference between theory and praxis. ... Thereby you want to say that praxis should be as unencumbered as possible by theory. Coming from you, this wish is quite intelligible. What you mean by praxis is private profit; what I mean by theory is justice.

Theorie und Praxis sind Eins wie Seele und Leib, und wie Seele und Leib liegen sie großenteils mit einander in Streit.

Nothing can be more idle than the opposition of theory to practice!

In theory there is no difference between theory and practice; in practice there is.

La teoria è quando si sa tutto e niente funziona. La pratica è quando tutto funziona e nessuno sa il perché. Noi abbiamo messo insieme la teoria e la pratica: non c'è niente che funzioni... e nessuno sa il perché!

As a rule, theory does not precede practice. Its role is to structure and codify already proven practice. Its role is to convert the isolated and “atypical” from exception to “rule” and “system,” and therefore into something that can be learned and taught and, above all, into something that can be generally applied.

As Yogi Berra said, “In theory there is no difference between theory and practice; in practice there is.

In theory there’s no difference between theory and practice. But, in practice, there is. — BENJAMIN BREWSTER, EPISCOPAL BISHOP

A theory is something nobody believes, except the person who made it. An experiment is something everybody believes, except the person who made it.

On theory: "I don’t know any theory. Knowing the theory does not mean anything. If we theoretically know what a human being is, but someone has never seen one, or if you have never had a relationship with a human being, you cannot know anything about human beings! I think that the best way to gain knowledge is through gaining experience and through connections... Look, if I approach an instrument theoretically, it will give me a theory, so therefore this will make cold music".

A theory is like medicine or government: often useless, sometimes necessary, always self-serving and, on occasion, lethal. It needs to be used with care, moderation and close adult supervision.

(…) Theories are neither right nor wrong. They are attempts at explaining the inexplicable. It is not the theory that matters, but the way it is being tested. (…) Experiment with any theory you like – if you are truly earnest and honest, the attainment of reality will be yours. (…) It is the earnestness that liberates and not the theory.

La Pratique parlait son langage positif à la Théorie dont la parole est toujours au Futur.