When I came to M.I.T. around 1920, the general mode of putting the questions concerning non-linear apparatus was to look for a direct extension of the notion of impedance which would cover linear as well as non-linear systems. The result was that the study of non-linear electrical engineering was getting into a state comparable with that of the last stages of the Ptolemaic system of astronomy, in which epicycle was piled on epicycle, correction upon correction, until a vast patchwork structure ultimately broke down under its own weight.

Just as the Copernican system arose out of the wreck of the over-strained Ptolemaic system, with a simple and natural heliocentric description of the motions of the heavenly bodies instead of the complicated and unperspicuous Ptolemaic geocentric system, so the study of non-linear structures and systems, whether electric of mechanical, whether natural or artificial, has needed a fresh and independent point of commencement.

CYBERNETICS, or control and communication in the animal and the machine, NORBERT WIENER, second edition, THE M.I.T. PRESS and JOHN WILEY & SONS, INC. PREFACE, viii.