The Role of Definitions in Science
THE SCIENTIST prides himself on the clarity and precision of the concepts he employs. Many minds see in accurate thought and speech the prime characteristic of every science, and it is the professional creed of the physicist and his interpreters that terms must not be used unless they are clearly defined. Like most creeds, however, this utterance has become hollow by reason of its being at times thoughtlessly proclaimed.
What has happened with respect to definitions in recent years may be summarized as follows: To ensure clarity and precision, scientists have done what appears obvious at first sight; they have insisted that every concept be defined in a single way. Then, realizing that there are in fact numerous good definitions of some physical concepts (for after all it does not matter in a fundamental sense whether we define time by reference to the sun or to a pendulum clock), they were at first perplexed; but soon, with single-minded determination, influential philosophers and scientists decreed the elimination of obnoxious definitions, leaving only Zuordnungssätze ( Carnap), operational definitions ( Bridgman), and the like. Controversies arose as to which of several definitions of a given physical quantity (force is a favored victim) was indeed the proper one, and physics teachers clustered into groups, each with an allegiance to its own set of recipes. As they looked at time-honored phrases, they found them meaningless, and they made the shocking discovery that great men had indulged in word play and circumlocution when they defined their terms. Even Newton committed the atrocious crime of circularity when he said: Mass is density times volume.--For what is density if not mass per unit volume?