Alonzo Church

“By the nature of a formal system, there can be no objection to the introduction of arbitrarily complex and involved rules of procedure, provided only that they are perfectly explicit.”

“Indeed, if there is any result, from any formal theory, which has been established by a proof of finite length, it is possible to find a proof of it in the simple theory of types.”

“There is no sound basis for preferring any one of the known systems of logic as being the one and only 'true' logic.”

“The only thing that might be said to have been a mistake in the intuitionistic mathematics was the choice of a name for it.”