Abstract
Of some fields it is difficult to tell whether they are sound or phony. Perhaps they are both. Perhaps the decision depends on the circumstances, and it changes with time. At any rate, it is not an objective fact like "the moon is made of green cheese." Some subjects start out with impeccable credentials, catastrophe theory for instance, and then turn out to resemble a three-dollar bill. Others, like dynamic programming, have to overcome a questionable background before they are reluctantly recognized to be substantial and useful. It is a tough world, even for the judgement-pronouncers.