Paul Needham

Developments in the application of quantum mechanics to the understanding of the chemical bond are traced with a view to examining the evolving conception of the covalent bond. Beginning with the first quantum mechanical resolution of the apparent paradox in Lewis’s conception of a shared electron pair bond by Heitler and London, the ensuing account takes up the challenge molecular orbital theory seemed to pose to the classical conception of the bond. We will see that the threat of delocalisation can be overstated, although it is questionable whether this should be seen as reinstating the issue of the existence of the chemical bond. More salient are some recent developments in a longstanding discussion of how to understand the causal aspects of the bonding interaction—the nature of the force involved in the covalent link—which are taken up in the latter part of the paper.

Late nineteenth‐century opponents of atomism questioned whether the evidence required any notion of an atom. In this spirit, Duhem developed an account of the import of chemical formulas that is clearly neutral on the atomic question rather than antiatomistic. The argument is supplemented with specific inadequacies of atomic theories of chemical combination and considerably strengthened by the theory of chemical combination provided by thermodynamics. Despite possible counterevidence available at the time, which should have tempered some of Duhem's concluding remarks, there was no atomic theory of chemical combination, which is wholly a product of the twentieth century. †To contact the author, please write to: Department of Philosophy, University of Stockholm, SE‐106 91 Stockholm, Sweden; e‐mail: [email protected].

The bulk of Duhem's writing which bears on the understanding of mixtures suggests he adopted an Aristotelian position which he opposed only to the atomic view. A third view from antiquity-that of the Stoics-seems not to be taken into account. But his lines of thought are not always as explicit as could be wished. The Stoic view is considered here from a perspective which Duhem might well have adopted. This provides a background against which his somewhat unorthodox Aristotelianism might be understood.

In 1904 Joachim published an influential paper dealing with 'Aristotle's Conception of Chemical Combination' which has provided the basis of much more recent studies. About the same time, Duhem developed what he regarded as an essentially Aristotelian view of chemistry, based on his understanding of phenomenological thermodynamics. He does not present a detailed textual analysis, but rather emphasises certain general ideas. Joachim's classic paper contains obscurities which I have been unable to fathom and theses which do not seem to be fully explained, or which at least seem difficult for the modern reader to understand. An attempt is made here to provide a systematic account of the Aristotelian theory of the generation of substances by the mixing of elements by reconsidering Joachim's treatment in the light of the sort of points which most interested Duhem.The work described in this paper was undertaken with a view to providing a basis for presenting, evaluating and criticising Duhem's understanding of what was for him modern chemistry. This latter project will be taken up on another occasion. I hope the present paper will be of some value to a broader philosophical readership in so far as it provides a fairly clear conception of matter which might be called Aristotelian, even if it is not precisely Aristotle's, and raises certain clear problems of interpretation. It may also be of interest to historians of chemistry in suggesting an analysis of the old chemical notion of a mixt independent of atomic theories

This paper traces the principal thematic developments in Aristotle’s conception of chemical substance as they bear on the evolution of the notion into modern times. A line of speculation is indicated about the interpretation of elemental proportions clearly raised by Aristotle’s discussion but not pursued in his extant writings. Apart from its historical interest, Aristotle’s discussion of substance and mixture has been taken up in contemporary systematic philosophy (Fine 1995), where it is treated as at best only relevant to ordinary, everyday views. This approach gains support from the contention that such views have been superseded by the molecular conception of chemical substance developed in 19th century science and extolled by advocates of the Kripke-Putnam conception of microessentialism (Kripke 1980, Putnam 1975). Duhem (1902), who well understood what would now be called the macroscopic theory of thermodynamics and its relevance to chemistry, had a different view, and the present discussion is much influenced by him. Certainly, Aristotle’s view stands in need of modification in the light of the understanding of mixtures provided by Gibbs’ phase rule (Gibbs 1948). But with a certain weakening, a central Aristotelian claim about mixtures still has some bearing.

ABSTRACT The idea that the extension of a chemical substance is fixed by determining what stands in the relation of being the same substance to a paradigm sample plays a substantial role in chemistry, and procedures of identification that don’t make direct use of the method can be traced back to ones that do. But paradigm samples are not typically selected by ostension, as in Putnam’s version of this procedure. The relevance of ostension is questioned after a discussion of the establishment of paradigm specimens in the analysis of some contents of crude oil and an examination of the general features of the same-substance relation that takes into account the temporal dependency and the consequent role of characteristic features of substances. 1Introduction 2Some Formal Properties of the Same-Substance Relation 3Characteristic Properties and Paradigm Samples 4Naming Substances Old and New 5Some Points of Comparison with Temperature 6Summary and Conclusion

This article was first published as “Notation atomique et hypothèses atomistiques”, Revue des questions scientifiques, 31 (1892), 391– 457. It is the second of a series of articles Duhem was to publish in the Catholic journal Revue des questions scientifiques, in which he presents his understanding of what can justifiably be said about the structure of chemical substances as captured by chemical formulas. The argument unfolds following a broadly historical development of events throughout the course of the century which was coming to a close as he wrote. He later reflected in his classic The Aim and Structure of Physical Theories – based in large part on articles which had appeared in the Revue – that “To give the history of a physical principle is at the same time to make a logical analysis of it” (p. 269). Logical analysis clearly dominates in the present article. The historical context was elaborated considerably in a later work, Le mixte et la combinaison chimique: Essai sur l’évolution d’une idée, which did not lead him to retract any aspect of his earlier position but provided a broader setting in which it could be elaborated. In particular, the Aristotelian influence, which is only hinted at here in some of the formulations (see especially the beginning of section VII) without mentioning Aristotle by name, is explicit in the later work, making Duhem’s own ontological conception a little clearer. A discussion of stereoisomerism, conspicuously absent in the present article, is also integrated into the later book. The same holds for Avogadro’s hypothesis.

The Aristotelian distinction between actual and potential presence of a substance in a mixture forms part of a conception of mixture which stands in contrast to atomist and Stoic theories as propounded by the ancients. But the central ideas on which these theories are built need not be combined and opposed to one another in precisely the ways envisaged by these ancient theories. This is well illustrated by Duhem, who maintained the Aristotelian idea that the original ingredients are only potentially, and not actually, present in a mixture, but who sided with the Stoics and against Aristotle on the possibility of co-occupancy. I have argued that the Stoic theory cannot dispense with some such notion as the Aristotelian conception of potentiality in allowing the elements to be actually present in a mixture. Here I suggest that some such Aristotelian notion must be at work in a more modern atomic conception of matter if this is to allow elemental substances to be actually present in compounds, which I think is how compounds are usually understood. Analogous issues arise regarding the status of solutions and their components.

The history of the hydrogen bond provides a good example of the of an important chemical concept. It illustrates the interplay between empirical and theoretical approaches to the problem of delimiting what has proved to be quite an elusive notion, with chemists whittling away at the particular sorts of case with a view to obtaining a precise, unitary concept. Even though there is a return to a more theoretically inspired notion in more recent research, empirical characterisations remain a feature of the report of a Task Group recently set up by the IUPAC to reconsider the definition of the hydrogen bond, and this situation—by no means unusual for chemical concepts and principles—is unlikely to change in the foreseeable future. These developments are reviewed in this paper, which includes an extended discussion of the enormous significance hydrogen bonding has for the philosopher’s standard example of a “natural kind”, water. There is little to suggest a reduction to what philosophers of physics are pleased to call fundamental principles, and the details raise further questions about what essentialists could possibly have in mind when talking about the microscopic essence of water

The various conclusions reached in this paper can be drawn together and briefly summarised in the following thesis: It is necessary to use variables ranging over times explicitly in the object language in the logical analysis of temporal reference in English. A discussion of Arthur Prior ideas, which are in direct opposition to those encompassed here, focuses on the principle that the point of view of the speaker dominates all subordinate clauses, which I maintain and Prior rejects. This leads me to oppose the Priorean approach of considering tenses along the lines of propositional modal operators and in particular to criticise the notion of a proposition with variable truth value. My discussion concerns not only tenses, but also dates, and seeks to provide an account of tenses and dates together in a unified framework.

This undergraduate textbook introduces some fundamental issues in philosophy of science for students of philosophy and science students. The book is divided into two parts. Part 1 deals with knowledge and values. Chap. 1 presents the classical conception of knowledge as initiated by the ancient Greeks and elaborated during the development of science, introducing the central concepts of truth, belief and justification. Aspects of the quest for objectivity are taken up in the following two chapters. Moral issues are broached in Chap. 4, which discusses some aspects of the use and abuse of science, taking up the responsibilities of scientists in properly conducting their business and decision-makers in their concerns with the import of science for society. Part 2 contrasts the view of scientific progress as the rejecting of old hypotheses and theories and replacing them with new ones, represented by Karl Popper, with the conception of progress as accumulating knowledge, saving as much as possible from older theories, represented by Pierre Duhem. A concluding chapter defends the natural attitude of taking the theories of modern science to be literally true, i.e. realism, in the face of arguments drawn partly from the history of scientific progress in criticism of this stance.

Some points are made about substance properties in their role of introducing mass terms. In particular, two conditions of distributivity and cumulativity of mass predicates expressing these properties are not the independent pair they first appear to be. A classification of macroscopic substance concepts is developed. This needs to be complemented in some way by the introduction of a modal qualification reminiscent of Aristotle's distinction between actual and potential presence of substances in a mixture. Consideration of the latter feature has prompted Joe Earley to raise the question of whether there is any salt in the sea. I try to argue that there is.

Davidson's account of singular causal statements as expressing relations between events together with his views on event identity lead to inferences involving causal statements which many of his critics find counterintuitive. These are sometimes said to be avoided on Kim's view of events, in terms of which this line of criticism is often formulated. It is argued that neither Davidson nor Kim offer a satisfactory account of events — an essential prerequisit for the relational theory — and an account of singular causal statements in terms of a modal sentential connective is advocated in place of the relational view. Such an account suffices to block the counterintuitive inferences without needing to resort to a theory of events. It is suggested that a theory of events might be built upon a connective account of singular causal statements, but no such theory is presented here

Davidson’s account of singular causal statements as expressing relations between events together with his views on event identity lead to inferences involving causal statements which many of his critics find counterintuitive. These are sometimes said to be avoided on Kim’s view of events, in terms of which this line of criticism is often formulated. It is argued that neither Davidson nor Kim offer a satisfactory account of events - an essential prerequisit for the relational theory - and an account of singular causal statements in terms of a modal sentential connective is advocated in place of the relational view. Such an account suffices to block the counter-intuitive inferences without needing to resort to a theory of events. It is suggested that a theory of events might be built upon a connective account of singular causal statements, but no such theory is presented here.

This book is about matter. It involves our ordinary concept of matter in so far as this deals with enduring continuants that stand in contrast to the occurrents or processes in which they are involved, and concerns the macroscopic realm of middle-sized objects of the kind familiar to us on the surface of the earth and their participation in medium term processes. The emphasis will be on what science rather than philosophical intuition tells us about the world, and on chemistry rather than the physics that is more usually encountered in philosophical discussions. It is the everyday science of matter characterised by differences of chemical substance that constitutes individuated macroscopic bodies of geological and biological complexity—the continuous matter of macroscopic theory and described by mass terms. The discussion might be characterised as descriptive metaphysics, being content, to paraphrase Strawson’s use of the term, to describe the structure of our scientific thought about the actual world. The method in the central chapters dealing with the nature of matter will be to pursue key steps in the historical development of scientific thought about chemical substance and related concepts with a view to tracing the emergence of a systematic ontological interpretation. Aristotle’s and the Stoics’ discussions of elements and mixtures, based on a continuous view of matter, bear some resemblance to modern, macroscopic conceptions and therefore have some interest as precursors to modern views as well as being of conceptual interest in their own right. Some of the issues they raised are still reflected in modern discussions, despite the considerable increase in complexity of the subject. Other ideas, such as the intimate connection between what modern science distinguishes as substance and phase, maintained their grip on the understanding of matter until the end of the eighteenth century. These are some of the important aspects of the properties of matter that have been neglected by linguistic concerns that have dominated the recent study of mass terms and which the present study seeks to redress. It will be of interest to see how the bounds of possibility are delimited by the laws governing the appropriate use of concepts refined for the purpose of describing the behaviour of matter. But the concern with modality will not stretch to venturing into the realms of metaphysical possibility governed by philosophical speculation about individual essences and underlying natures. Like many contemporary discussions of material objects, this one relies heavily on mereology. Unlike several such discussions, this one adheres to the classical principles of mereology governing the usual dyadic relations of part, overlapping, etc. and the operations of sum, product and difference. These principles apply to the mereological structure of regions of space, intervals of time, processes and quantities of matter. Material objects that gain and lose matter are not understood to gain and lose parts and don’t call for a modification of the classic dyadic mereological relations to triadic relations with the introduction of a third term referring to time. Rather, a distinction is drawn between quantities of matter, which don’t gain or lose parts over time, and individuals, which are typically constituted of different quantities of matter at different times. The proper treatment of the temporal aspect of the features of material objects is a central issue in this book. The topics falling under this heading are addressed by investigating the conditions governing the application of predicates relating time and other entities. Of particular interest here are relations between quantities of matter and times expressing substance kind, phase and mixture.

Robert Deltete and Anastasios Brenner have provided a thorough examination of my translation of Duhem’s Le mixte et la combinaison chimique (1902) and associated essays. I am very grateful for their efforts and gratified that such competent reviewers should be generally positive. They provide an overview of relevant aspects of Duhem’s life and work, which may serve to introduce him to readers of this journal and promote interest in Duhem studies. They also raise and answer some questions about the interpretation and evaluation of Duhem’s work, make some points of criticism of my choice of material and question certain points of translation. The editor has suggested that I make a response, and I shall take up some issues in these three areas. Since Duhem’s views play a central role in the development of the concept of chemical substance which I have worked on in recent years, I will make several references to my own publications.

A general analysis of reduction is as important to critics who deny reductionist claims as to their advocates. Nagel’s analysis continued to find favour amongst such critics after advocates sought alternatives—often attempted generalisations of perceived specific paradigm cases of reductive identification, such as temperature and mean molecular kinetic energy. The pros and cons of Nagel’s account are discussed, but the difficulties are not satisfactorily overcome by approaches advanced by Causey, Spector and Beckermann. Although no general account is settled upon, temperature is considered in some detail and found not to provide the paradigm case of reduction taken to motivate these alternatives.

Duhem is perhaps the last active scientist to have produced a philosophi- cal text, and TheAim and Structure of Physical Theory retains its status as one that every textbook writer in the philosophy of science has to take into consideration. Several of Duhem’s other books have since appeared in English translation, but the Essays in the History and Philosophy of Science is the first collection of Duhem’s papers to appear in English. Commentators have oRen pointed out that the roots of Duhem’s main philosophical work are to be found in a series of articles he wrote in the Catholic journal, Revue des Questions Scientijiques, during the first part of the 1890s, and it is not before time that these should be made available in English. In fact, the editors of the Essays have done us the greater ser- vice of including some of these seminal papers in a broader selection from Duhem’s shorter pieces, ranging over the years from 1892 to 1915 and covering his interests in the history of science and the relation between science and religion, as well as the philosophy of science. In the latter cat- egory, there is a nice little essay, “The Nature of Mathematical Reason- ing” from 1912, in which he takes issue with Poincark’s views on math- ematical induction, a review of Mach’s The Science of Mechanics (1903) and “Logical Examination of Physical Theory” - the section dealing with his philosophy of science from the submission he wrote in 1913 in sup- port of his membership of the Academie des Sciences. Like the latter, the last two chapters of To Save the Phenomena (1908) and “Some Reflec- tions on German Science” (1915) have already appeared in English. Of the remaining nine essays, eight appear, as far as I’m aware, for the first time here in English, while the “lightly edited” “History of Physics” origi- nally appeared in English.

Gibbs’s phase rule treats mixtures by relating the number of independent variables governing their state to the numbers of phases and independent substances. For the case of a single substance, it provides a criterion of purity. But where more substances are involved, the notion of independent substance is less readily understood. Textbook writers sometimes use algebraic terminology in ways that are suggestive but cannot be taken as literally accurate. I suggest that a mereological interpretation applies to these cases, as it captures more concisely the insights underlying the use of algebraic ter- minology and illuminates the general notion of substance.