Hasok Chang

Historians often feel that standard philosophical doctrines about the nature and development of science are not adequate for representing the real history of science. However, when philosophers of science fail to make sense of certain historical events, it is also possible that there is something wrong with the standard historical descriptions of those events, precluding any sensible explanation. If so, philosophical failure can be useful as a guide for improving historiography, and this constitutes a significant mode of productive interaction between the history and the philosophy of science. I illustrate this methodological claim through the case of the Chemical Revolution. I argue that no standard philosophical theory of scientific method can explain why European chemists made a sudden and nearly unanimous switch of allegiance from the phlogiston theory to Lavoisier's theory. A careful re-examination of the history reveals that the shift was neither so quick nor so unanimous as imagined even by many historians. In closing I offer brief reflections on how best to explain the general drift toward Lavoisier's theory that did take place

Customary discussions of quantum measurements are unrealistic, in the sense that they do not reflect what happens in most actual measurements even under ideal circumstances. Even theories of measurement which discard the projection postulate tend to retain two unrealistic assumptions of the von Neumann theory: that a measurement consists of a single physical interaction, and that the topic of every measurement is information wholly contained in the quantum state of the object of measurement. I suggest that these unrealistic assumptions originate from an overly literal interpretation of the operator formalism of quantum mechanics. I also suggest, following Park, that some issues can be clarified by distinguishing the sense of the term ''''measurement'''' occurring in the quantum-mechanical operator formalism, and the sense of ''''measurement'''' that refers to actual processes of gaining information about the physical world.

I propose a reformulation of realism, as the pursuit of ontological plausibility in our systems of knowledge. This is dubbed plausibility realism, for convenience of reference. Plausibility realism is non-empiricist, in the sense that it uses ontological plausibility as an independent criterion from empirical adequacy in evaluating systems of knowledge. Ontological plausibility is conceived as a precondition for intelligibility, nor for Truth; therefore, the function of plausibilty realism is to facilitate the kind of understanding that is not reducible to mere description or prediction. Difficulties in making objective judgements of ontological plausibility can be ameliorated if we adhere to the most basic ontological principles. The workings of plausibility realism are illustrated through a detailed discussion of how one ontological principle, which I call the principle of single value, can be employed with great effect. Throughout the paper the discussion draws on concrete examples from the history of science.

I present philosophical reflections arising from a study of laboratory measurement methods in quantum physics. More specifically, I investigate three major methods of measuring kinetic energy, from the period during which quantum physics was developed and came to be widely accepted: magnetic deflection, electrostatic retardation, and material retardation. The historical material serves as a provocative focus at which many broader philosophical topics come together: the empirical testing of theories, the universal validity of physical laws, the interaction between theoretical and experimental traditions, incommensurability, meaning and definition, realism and instrumentalism, the process of scientific change, and the unity of science. ;I begin the discussion by noting that the measurement methods in question were based on classical theory. Chapter 1 asks how the classical reasoning in measurements can be interpreted in quantum-mechanical terms, and concludes that only a "surface interpretation" is possible, since the classical methods involve many assumptions that conflict with quantum mechanics. Chapter 2 attempts to give a quantitative assessment of the inaccuracies that might result from using the "incorrect" classical theory in the design of measurement methods. Chapter 3 asks how we can know whether a measurement method is reliable, and investigates how different methods of measuring the same quantity can ground each other; this mutual grounding is also seen as a process of concept-formation. Chapter 4 argues that the customary quantum theories of measurement do not describe actual measurements well, and originate from an overly literal interpretation of the operator formalism of quantum mechanics. Chapter 5 examines how the classically reasoned measurement methods were incorporated into quantum physics; that history suggests a model of scientific development which can introduce fundamental changes while preserving much continuity with the old tradition. Chapter 6 develops a philosophical framework which allows a synthetic view of the concrete results presented in the earlier chapters: my work is an attempt to establish "conceptual coherence," creating and clarifying noncontradictory connections among the various conceptual activities that make up quantum physics