The case of the complex numbers is a good illustration of
what was happening. Classical mathematics never felt at ease with the complex numbers, for it lacked
a suitable “interpretation” of them, and as a result there were nagging doubts as to whether such things
really “existed.” Real numbers may be interpreted as lengths or quantities, but the square root of a
negative real number—this did not seem to correspond to anything in the real world or in our intuition
of number. Yet the system of the complex numbers arises in a most natural way—as the smallest
number system which contains the real numbers and includes the roots of every algebraic equation
with real coefficients; whether or not the complex numbers have a physical or psychological
counterpart seems irrelevant.