Thus mathematics may be defined as the subject in
which we never know what we are talking about, nor whether what we are
saying is true. People who have been puzzled by the beginnings of
mathematics will, I hope, find comfort in this definition, and will
probably agree that it is accurate."
(Bertrand Russell)

From "Recent Work on the Principles of Mathematics
in International Monthly, 4 (July, 1901), 83101.
(Collected Papers, v3, p.366;
revised version in Newman's World of Mathematics, v3, p. 1577.)
EDIT ADD