The Operational Imperative: Sense and Nonsense in Operationism

Several important terms in biology have recently been criticized for not being "operational." In this paper the course of operationism in physics, psychology and genetics is sketched to show what effect this particular view on the meaning of scientific terms had on these disciplines. Then the biological species concept and the concept of homology are examined to see in what respects they are or are not "operational." One of the primary conclusions of this investigation is that few terms in science are completely operational or completely nonoperational. Some scientific terms, especially theoretical terms, are a good deal less operational than others; but, far from being regrettable, this situation is essential if theoretical terms are to fulfill their systematizing function and if scientific theories are to be capable of growth. Biologists frequently assert that the need in biology for operational definitions, concepts and procedures is imperative. However, what these biologists mean by "operational" ranges from admirable good sense to utter nonsense. At one end of the spectrum, a concept is operational if in some instances there are ways of discovering if the concept is applicable. At the other end, the meaning of the concept is supposedly equivalent to the set of operations used to test its applicability. Surreptitious vacillation between these two extremes has been characteristic of the movement termed "operationism"1 since its very inception. The purpose of this paper is first, to describe the role played by operationism in physics and psychology, and then to examine various biologists' notions of operationism to see exactly how appropriate they are for actual biological practice. OPERATIONISM IN PHYSICS In 1927 P. W. Bridgman in his famous treatise The Logic of Modern Physics suggested that a fruitful way of looking at Einstein's special theory of relativity was to regard the theory as substituting "opera1 The terms "operationism" and "operationalism" are used interchangeably to refer to the thesis made popular by P. W. Bridgman. Bridgman himself abhorred the terms. tional definitions" of concepts like length and non-local simultaneity for definitions in terms of properties: We may illustrate by considering the concept of length: what do we mean by the length of an object? We evidently know what we mean by length if we can tell what the length of any and every object is, and for the physicist nothing more is required. 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: that is, the concept of length involves as much as and nothing more than the set of operations by which length is determined. In general, we mean by any concept nothing more than a set of operations; the concept is synonymous with the corresponding set of operations. Bridgman's thesis is both radical and poorly expressed. Synonymy is a relation which holds between linguistic entities. Two words or two statements can be synonymous, but a concept cannot be synonymous with a set of operations. Bridgman might have expressed himself better had he said that a concept such as length denotes a set of operations, not a property of the objects being measured. And what is more, the meaning of the concept is this set of operations. Bridgman's thesis is radical because usually the intension of a concept is considered to be its meaning. One of the main reasons for trying to formulate operational definitions is to insure the objectivity of science. If a scien-