Campbell, Norman Robert

Campbell made important contributions to philosophy of science in the 1920s, influenced by Poincaré, Russell and his own work in physics. He produced pioneering analyses of the nature of physical theories and of measurement, but is mainly remembered for requiring a theory, for example, the kinetic theory of gases, to have an 'analogy', that is, an independent interpretation, for example, as laws of motion of a swarm of microscopic particles. The British philosopher of science Norman Robert Campbell, who became a Fellow of Trinity College Cambridge in 1904, was also an experimental physicist, and worked on the research staff of the British General Electric Company from 1919 to 1944. His main contribution to philosophy, published in 1920, is his account of how physical theories explain laws. It maintains an absolute distinction between laws relating observable properties of objects, on which agreement can be achieved, and theories used to explain them. It could allow a weaker distinction, letting accepted theories come to state laws needing further explanation. But only an implausible view of the significance of the distinction can save its claim that theories need analogies. Campbell's account of theories credits them with three components, illustrated by a simplified version of the kinetic theory of gases. First there is a theory's 'hypothesis', its mathematical propositions, empirically uninterpreted. Then there is a 'dictionary', linking terms of the hypothesis to observable terms used to state the laws the theory explains. Thus in his example the dictionary identifies the volume V, mass M, pressure P and absolute temperature T of a gas with combinations of constants and variables postulated by the hypothesis: for example, V = l 3, where l is a constant, M = nm, where m is a constant and 3n the number of variables dependent on the independent variable t (time). This hypothesis and dictionary entail the perfect gas law, PV / T .