The Science behind C. I. Lewis’s Pragmatic Conception of the A Priori

David J. Stump

Philosophy, USF

C. I. Lewis’s pragmatic conception of the a priori refers to three conceptual areas, logic, sentences that are true by definition, and some elements of physical theories. The laws of physics present the most interesting part of Lewis’s pragmatic theory of the a priori. Lewis accepts the Kantian point that certain principles constitute a science in the sense that they are necessary preconditions and that they thus make a science possible: “The fundamental laws of any science—or those treated as fundamental—are a priori because they formulate just such definitive concepts or categorical tests by which alone investigation becomes possible” (Lewis 1923/1970, 234-235). Although the constitutive elements function as a priori statements, they are not fixed and must only meet a pragmatic test of usefulness. It is possible that different fundamental laws could play the same role. Therefore, revolutionary changes in science can appear as changes in fundamental concepts and the role of these concepts in knowledge is fundamental in Lewis’s philosophy of science: “Empirical knowledge arises through conceptual interpretation of the given” (Lewis 1929, 37). It is these conceptual interpretations that are the focus of Lewis’s theory of the a priori. In both “The Pragmatic Theory of the A Priori” and in Mind and World Order, Lewis uses a single scientific example, the conventionality of simultaneity, to explain his theory. The example and his long quote from Einstein are central to his presentation of the pragmatic theory of the a priori and show the extent to which the theory was developed with science in mind and, indeed, the extent to which it depends on the Einstein example to gain plausibility. The fact that Lewis offers only one example and that it turns out to be a controversial one weakens his argument for the pragmatic a priori in science. However, it is important to recognize that Lewis sees his project as following directly from advances in mathematics and physics in the early twentieth century (Lewis 1929, vii-viii). Changes in mathematics and physics led to new philosophical thinking about the a priori and thus to alternatives to the positivist’s rejection of the a priori. In this sense Lewis was presenting an alternative philosophy of science which is similar to the early work of Reichenbach (1920), the recent work of Friedman (2001) and others. I trace the genealogy of Lewis’s theory and compare its strengths and weaknesses to similar views.