Uit: Language in Thought and Action, door S.I. Hayakawa.

Chapter 10 

Operational Definitions

Another way to keep extensional levels in mind, when definitions are called for, is to use what physicist P. W. Bridgman called "operational definitions." As he says,
 
  To find the length of an object, we have to perform certain physical operations. The concept of length is therefore fixed when the operations by which length is measured are fixed. ... In general, we mean by any concept nothing more than a set of operations; the concept is synonymous with the corresponding set of operations.1

    The operational definition, then, as Anatol Rapoport explains, is one that tells you "what to do and what to observe in order to bring the thing defined or its effects within the range of one's experience." He gives the following simple example of how to define "weight": go to a railroad station or drugstore, look for a scale, stand on it, put in a penny, read the number at which the pointer comes to rest. That is your weight. But supposing different scales give different readings? Then your weight can be said to be within the range of, say, 140 to 145 pounds. With more accurate scales you might get closer readings, such as 142 pounds plus-or-minus one. But there is no "property" called weight that exists apart from the operations measuring it. As Rapoport says, "If the only way we can be aware of the amount of weight is by means of the scale, then the very definition of weight has to be in terms of the scale." 3
    Such, then, is the scientific, or "operational," point of view towards definition---one that attempts rigidly to exclude non-extensional, non-sense statements. We can extend this idea from science to the problems of everyday life and thought. Just as there is no such thing as "length" apart from the operations by which length is measured, just as there is no "weight" apart from the operations by which weight is determined, there is likewise no "democracy" apart from the sum-total of democratic practices, such as universal franchise, freedom of speech, equality before the law, and so on. Similarly, there is no such thing as "brotherhood" apart from brotherly behavior, nor "charity" apart from charitable actions.
    The operational point of view does much to keep our words meaningful. When people say things like, "Let's have no more of progressive methods in our schools," "Let's get back to sound business principles in running our county government," "Let's try to do the Christian thing," "Let's put father back as head of the family," we are entitled to ask, "what do you mean - extensionally speaking? To ask this question often - of ourselves as well as of others-is to do our bit towards reducing the vast amount of non-sense that is written, spoken, and shouted in this incredibly garrulous world.
    The best examples in everyday life of operational definitions are to be found in cookbooks, which describe the operations by means of which the entity defined may be extensionally experienced. Thus: "Steak Diane. Slice tenderloin beef very thin and give it a few whacks with a meat mallet to flatten it even more; sprinkle with salt and pepper to taste. Have your pan very hot. . . ." (The Sunset Cook Book.) Writers and speakers would do well to study cookbooks occasionally to increase the clarity and verifiability of their utterances.

1 The Logic of Modern Physics (1927), p. 5.


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