 Especially important for Bridgman’s thinking was Albert Einstein’s special theory of relativity. Bridgman credited an unexpected teaching assignment in 1914 for his first real encounter with special relativity, which gave him considerable distress as he tried to clarify the confusing conceptual situation surrounding the theory (Bridgman in Frank 1956, 76). At the heart of special relativity was Einstein’s recognition that judging the simultaneity of two events separated in space required a different operation from that required for judging the simultaneity of two events happening at the same place. Fixing the latter operation was not sufficient to fix the former, so a further convention was necessary, which Einstein supplied in the form of his operation of sending light beams from each of the events in question to the midpoint between their locations, to see if they arrive there at the same time. How superior this way of thinking was, compared to Isaac Newton’s declaration that he would “not define Time, Space, Place or Motion, as being well known to all” (quoted in Bridgman 1927, 4)! Bridgman felt that all physicists, including himself, had been guilty of unthinking uses of concepts, especially on the theoretical side of physics.