“I think that it is a relatively good approximation to truth which is much too complicated to allow anything but approximations, that mathematical ideas originate in empirics. But, once they are conceived, the subject begins to live a peculiar life of its own and is...governed by almost entirely aesthetical motivations. In other words, at a great distance from its empirical source, or after much 'abstract' inbreeding, a mathematical subject is in danger of degeneration. Whenever this stage is reached the only remedy seems to me to be the rejuvenating return to the source: the reinjection of more or less directly empirical ideas.”
