ARE PHYSICAL MAGNITUDES OPERATIONALLY DEFINABLE? (1959)

The question chosen as title of this paper may strike the reader as peculiar. For it is often said that an operational definition of a concept is a definition in terms of operations of measurement. To be an operationist, many scientists would say, is to insist that scientific concepts be made precise and empirically applicable by defining them in terms of measuring operations. Does it not follow, then, that, if any concepts are operationally definable, then concepts of physical magnitudes are? However, the widely used term “operational definition” needs clarification. I shall specify in the course of this paper a sense in which such terms as “length,” “mass,” “temperature,” etc. are not operationally definable insofar as they enter into the mathematical formulation of physical laws; but I will also specify a sense in which they must be operationally definable if they are to have any physical significance.