Whenever we write an axiom, a critic can say that the axiom is true only in a certain context. With a little ingenuity the critic can usually devise a more general context in which the precise form of the axiom doesn't hold. [...] There simply isn't a most general context.
"Generality in Artificial Intelligence" (1971–1987), ACM Turing Award Lectures: The First Twenty Years, ACM Press, 1987, ISBN 0201077949