Tools of the Trade: Thought Experiments Examined By Tamar Gendler t the end of the last century, Ernst Mach coined a term to describe a particular technique of scientific investigation, a mental analogue to physical experiment which he dubbed "Gedankenexperiment."l A According to Mach, this method is central to the history of science; its greatest practitioners include Aristotle and Galileo, and its careful employ- ment "led to enormous changes in our thinking and to an opening up of most important new paths of inquiry."z In the century that followed, Mach's term (and its English translation) showed up occasionally in the philosophy of science literature, most notably, perhaps, in Karl Popper's "On the Use and Misuse of Imaginary Experiments, Especially in Quantum Theory,"3 and in Thomas Kuhn's, "A Function for Thought experiment^."^ Discussions of the technique - in science and in philosophy - made sporadic appearances on the pages of philosophy journals, each year's Philosophers' Index sporting some dozen entries under "Thought Experiment." Then, in the mid-1980s, the Zeitgeist smiled upon thought experiments; they were explicitly recognized as a central technique in analytic philosophy, and self-conscious philosophical scrutiny was directed upon them.5 In the Spring of 1986, Tamara Horowitz and Gerald Massey organized a conference at the University of Pittsburgh on "The Place of Thought Experiments in Science and ~ h i l o s o ~ h ~ . " ' along with several others inspired by it, are collected in Thought Experiments in Science and Philosophy, published in 1991. A year later, Roy Sorensen published his Thought Experiments, a detailed ten-chapter discus- sion of thought experiments in philosophy and science, in which he defends their con- tinuity with physical experiment, and adduces numerous arguments in favor of their philosophical legitimacy. Sorensen's style is chatty and unpre- tensious, full of striking turns of phrase and colloquialisms: "I am bullish on the comparison;" "this protoype gives us a bum steer;" "Wittgenstein discourages fas- cination with mental freak shows;" "tradi- tional metaphysicians scoffed at Meinong's he papers given at that conference,