 Bridgman’s ambivalence about conceptual unity elicited a serious worry about the systematic import of scientific concepts and theories, most astutely expressed by Hempel (1966, 91–97). Bridgman’s skeptical caution would result in an intolerable fragmentation of science, Hempel argued. It would result in “a proliferation of concepts of length, of temperature, and of all other scientific concepts that would not only be practically unmanageable, but theoretically endless.” Hempel’s worry was that Bridgman’s quest for safety was blinding him to one of the ultimate aims of science, “namely the attainment of a simple, systematically unified account of empirical phenomena” (Hempel 1966, 94). Along similar lines, Lindsay (1937, 458) had earlier argued that “such an isolation of concepts would defeat the very aim of physical science, which is to provide a simple and economical description” of physical experience “in terms of a minimum number of concepts”. Bridgman had serious doubts about the plausibility of such a simple, unified account of nature, as I will explain further in Section 3.4. But Hempel and others could genuinely envisage it. Hempel noted that with the development of science there was a continually growing and thickening network of “nomic threads” linking various “knot-concepts” with each other as further empirical laws were discovered. Hempel argued that it was essential to keep this thickening conceptual network systematic and simple; to that end, “concept formation and theory formation must go hand in hand” (Hempel 1966, 97). That, in turn, often necessitated “a modification of the operational criteria originally adopted for some of the central concepts” (Hempel 1966, 95). Operationalism would stand in the way of such flexibility.