Hasok Chang

Many of the experiments that produced the empirical basis of quantum mechanics relied on classical assumptions that contradicted quantum mechanics. Historically this did not cause practical problems, as classical mechanics was used mostly when it did not happen to diverge too much from quantum mechanics in the quantitative sense. That fortunate circumstances, however, did not alleviate the conceptual problems involved in understanding the classical experimental reasoning in quantum-mechanical terms. In general, this type of difficulty can be expected when a coherent scientific tradition undergoes a theoretical upheaval. The problem may be circumvented through the use of phenomenological theory in experimentation during the period of theoretical instability.

Scientific progress remains one of the most significant issues in the philosophy of science today. This is not only because of the intrinsic importance of the topic, but also because of its immense difficulty. In what sense exactly does science makes progress, and how is it that scientists are apparently able to achieve it better than people in other realms of human intellectual endeavour? Neither philosophers nor scientists themselves have been able to answer these questions to general satisfaction.

This book exhibits deep philosophical quandaries and intricacies of the historical development of science lying behind a simple and fundamental item of common sense in modern science, namely the composition of water as H2O. Three main phases of development are critically re-examined, covering the historical period from the 1760s to the 1860s: the Chemical Revolution, early electrochemistry, and early atomic chemistry. In each case, the author concludes that the empirical evidence available at the time was not decisive in settling the central debates and therefore the consensus that was reached was unjustified or at least premature. This leads to a significant re-examination of the realism question in the philosophy of science and a unique new advocacy for pluralism in science. Each chapter contains three layers, allowing readers to follow various parts of the book at their chosen level of depth and detail. The second major study in "complementary science", this book offers a rare combination of philosophy, history and science in a bid to improve scientific knowledge through history and philosophy of science.

Acidity provides an interesting example of an everyday concept that developed fully into a scientific one; it is one of the oldest concepts in chemistry and remains an important one. However, up to now there has been no unity to it. Currently two standard theoretical definitions coexist ; the standard laboratory measure of acidity, namely the pH, only corresponds directly to the Br⊘nsted-Lowry concept. The lasting identity of the acidity concept in modern chemistry is based on the persistence of the quotidian concept. This is suggestive for considerations of other scientific concepts.

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.

The direct use of a physical law for the purpose of measurement creates a problem of circularity: the law needs to be empirically tested in order to ensure the reliability of measurement, but the testing requires that we already know the value of the quantity to be measured. This problem is discussed through some detailed examples of energy measurements in quantum physics; three major methods are analyzed in their interrelation, with a focus on the method of “material retardation.” It seems that the only reasonable solution is to establish the law needed for the measurement by relying on an alternate method of measurement. This solution is also circular, since it amounts to letting different measurement methods justify each other. However, this circularity can be fruitful for the process of concept building; meaning can be created in a web of interconnected measurement methods.

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.

What can we conclude from a mere handful of case studies? The field of HPS has witnessed too many hasty philosophical generalizations based on a small number of conveniently chosen case studies. One might even speculate that dissatisfaction with such methodological shoddiness contributed decisively to a widespread disillusionment with the whole HPS enterprise. Without specifying clear mechanisms for history-philosophy interaction, we are condemned to either making unwarranted generalizations from history, or writing entirely "local" histories with no bearing on an overall understanding of the scientific process. I propose a move away from the habit of viewing historical cases as an inductive evidence-base for general philosophical theses. The relation between historical and philosophical studies should not be seen as one between the particular and the general, but as a relation between the concrete and the abstract. An abstract framework is necessary for telling any concrete story at all. In this paper I explore how doing concrete history can help our abstract philosophizing. In the absence of ready-made philosophical concepts appropriate for understanding a given historical episode, the historian is compelled to craft new abstract philosophical concepts. Therefore, history-writing can be a very effective method of philosophical discovery. I will illustrate these claims through a discussion of two investigations in HPS from my own recent and current work: (1) temperature measurement and epistemic iteration; (2)constitution and laboratory practices in the Chemical Revolution. (This will also raise, and solve, a problem of reflexivity: how can we use case studies to show how to go beyond case studies?).

I seek to provide a systematic and comprehensive framework for the description and analysis of scientific practice—a philosophical grammar of scientific practice, ‘grammar’ as meant by the later Wittgenstein. I begin with the recognition that all scientific work, including pure theorizing, consists of actions, of the physical, mental, and ‘paper-and-pencil’ varieties. When we set out to see what it is that one actually does in scientific work, the following set of questions naturally emerge: who is doing what, why, and how? More specifically, we must arrive at some coherent philosophical accounts of the following elements of scientific practice: the agent—free, embodied, and constantly in second-person interactions with other agents; the purposes and proximate aims of the agent; types of activities that the agent engages in; ontological principles necessarily presumed for the performance of particular activities; instruments and other resources that the agent pulls together for the performance of each activity. After sketching the general framework, I also give some illustrative contrasts between the more traditional descriptions of scientific practice and the kind of descriptions enabled by the proposed framework.

A popular and plausible response against Laudan's “pessimistic induction” has been what I call “preservative realism,” which argues that there have actually been enough elements of scientific knowledge preserved through major theory‐change processes, and that those elements can be accepted realistically. This paper argues against preservative realism, in particular through a critical review of Psillos's argument concerning the case of the caloric theory of heat. Contrary to his argument, the historical record of the caloric theory reveals that beliefs about the properties of material caloric, rejected by subsequent theories, were indeed central to the successes of the caloric theory. Therefore caloric remains a favorable case for Laudan. Further, I argue that even confirmed cases of preservation do not warrant an inference to truth.

An interesting case of the complex interaction between theory and experiment can be found in many experiments in quantum physics employing classical reasoning. It is expected that this practice would lead to quantitative inaccuracy, unless the measurements' results were averaged. Whether or not this inaccuracy is significant depends critically on the details of the particular experimental situation. The example of Millikan's photoelectric experiment, in which he obtained a precise value of Planck's constant, provides a good case for illustrating the process of estimating the inaccuracy resulting from the classical-quantum discrepancy. In the case of Millikan's experiment, it seems that a significant inaccuracy was avoided because of fortunate coincidences. In general, in the absence of a careful analysis, it is impossible to say whether the use of classical reasoning interferes with the accuracy of a quantum-physical experiment.

This chapter advances a contextual view of evidence, through a reconsideration of Hempel's paradox of confirmation. The initial view regarding Hempel's paradox is that a non-black non-raven does confirm ‘All ravens are black’, but only in certain contexts. The chapter begins by reformulating the paradox as a puzzle about how the same entity can have variable evidential values for a given proposition. It then offers a three-stage solution to the reformulated paradox. The situation makes better sense when we reach a deeper propositional understanding of evidence, recognising that each entity can be represented in multiple observational propositions. Some anti-contextualist intuitions can be defused by distinguishing two different senses of the word ‘evidence’, one applying to objects or events and the other applying to propositions; only the latter is relevant to inference. A fuller understanding comes from analysing the constitution and use of evidence in terms of epistemic action. These reflections on the ravens paradox suggest a general philosophical framework more suitable for understanding the function of evidence in scientific and everyday practices.

I develop a concept of observability that pertains to qualities rather than objects: a quality is observable if it can be registered by human sensation (possibly with the aid of instruments) without involving optional interpretations. This concept supports a better description of observations in science and everyday life than the object-based observability concepts presupposing causal information-transfer from the object to the observer. It also allows a rehabilitation of the traditional empiricist distinction between observations and their interpretations, but without a presumption that observations are infallible. Using this concept of observability, I also propose a re-formulation of constructive empiricism that is easier to defend against realist attacks, while open to reasonable realist intuitions.

Why do some epistemic objects persist despite undergoing serious changes, while others go extinct in similar situations? Scientists have often been careless in deciding which epistemic objects to retain and which ones to eliminate; historians and philosophers of science have been on the whole much too unreflective in accepting the scientists’ decisions in this regard. Through a re-examination of the history of oxygen and phlogiston, I will illustrate the benefits to be gained from challenging and disturbing the commonly accepted continuities and discontinuities in the lives of epistemic objects. I will also outline two key consequences of such re-thinking. First, a fresh view on the (dis)continuities in key epistemic objects is apt to lead to informative revisions in recognized periods and trends in the history of science. Second, recognizing sources of continuity leads to a sympathetic view on extinct objects, which in turn problematizes the common monistic tendency in science and philosophy; this epistemological reorientation allows room for more pluralism in scientific practice itself.

In Inventing Temperature, Chang takes a historical and philosophical approach to examine how scientists were able to use scientific method to test the reliability of thermometers; how they measured temperature beyond the reach of thermometers; and how they came to measure the reliability and accuracy of these instruments without a circular reliance on the instruments themselves. Chang discusses simple epistemic and technical questions about these instruments, which in turn lead to more complex issues about the solutions that were developed.