Paul Needham

An exposition of Pierre Duhem’s formulation of the structure of chemical substances as expressed by their formulas is given, presenting it as a development of his essentially Aristotelian view of mixtures. Duhem’s masterly development of the subject displays an eye for logical clarity familiar from his work in thermodynamics but applied here to the extraction of what he regarded as true from the history of chemistry. Though no longer defensible, the account has a conceptual interest in its own right and illuminates a less frequently discussed side of Duhem’s views.

In response to difficulties in understanding the notion of chemical substance at issue in Gibbs’ phase rule, there is a long tradition of reformulating the simple statement of the rule. The leading idea is to rewrite the rule with a term for the number of substances actually present and to introduce additional terms making explicit the various kinds of restrictions which in the original formulation are taken to be incorporated into Gibbs’ notion of the number of independent substances. Although the number of independent substances cannot in general be interpreted as the number of substances actually present, it is not an entirely derivative concept as the authors of the reformulations sometimes seem to presuppose. In particular, it is doubtful whether the number of substances actually present is a clearly delimited concept which can be determined prior to the application of the phase rule. In that case, the phase rule provides a useful source of information for the determination of the number and nature of the substances actually present in a mixture which should be properly reflected in an adequate interpretation of Gibbs’ notion of independent substances. For this purpose, I propose a mereological interpretation of the way independent substances are related to the substances actually present which makes sense of the fact that the former are not uniquely fixed but can be chosen from the latter in several ways

Prima facie, there are two kinds of expression used in English to make reference to time: those involving explicit mention of time and temporal ordering relations, and tenses involving no such explicit reference. Taking as a criterion of adequacy the unification of both these aspects, a systematization is proposed (owing much to Reichenbach) which provides a characterization of tenses. The theory is not based on the notion of a proposition with variable truth value which formed the cornerstone of Arthur Prior’s work. His conception receives a good deal of criticism, ultimately on the ground that relativising to exactly one time is inadequate. We don’t know in advance whether or not no time of perhaps more than one time is relevant, and where this is the case, the analysis cannot be reduced to propositions true at just one time.

The historical development of the understanding of water is traced in the light of the development of the general concept of chemical substance. From the times of the earliest known ancient Greek philosophers, water has played a central role in the conception of the material constitution of the world. But it was Aristotle who developed the most sophisticated understanding of water to have come down to us from the ancients. He viewed it as part of an intricate and systematic theory of chemical substance, which classified water as an element along with earth, fire and air. His view exerted a considerable influence on Arabic and European thinkers throughout the Middle Ages, and wasn’t successfully challenged until the eighteenth century. After Lavoisier, it was recognised that water, though unlike air a single substance and not a mixture, is neither an element nor always liquid. General features of chemical substances, distinguishing elements, compounds and mixtures, were elaborated in a general theory and harmonised with the mechanical features of matter towards the end of the nineteenth century. Finally, the continuous conception of matter underlying the Aristotelian view, which had been unsuccessfully challenged in the seventeenth century, was definitely overturned in the twentieth century, and the intricate microstructure of water was revealed.

Are there events? If so, how are they to be conceived? A line of argument motivating ontological commitment to what I prefer to call processes is presented, drawing primarily on the development of the elementary understanding of thermal processes, but pointing to a broader view by analogical extension. Suggestions are made for an approach to the mereological structure of processes, and some comments are offered of linguistic distinctions sometimes applied to processes and to modal features of events mentioned in the literature.

Classical atoms—“part-less, ontologically irreducible simples” as the conference flyer puts it—are not the atoms of modern chemistry and analogies with the latter can be construed in various ways. They have figured in the historical development of concepts of chemical affinity but without, as Alan Chalmers and I have independently argued, making any significant contribution to empirically justified theories. A purely combinatorial conception of the formation of compounds by juxtaposing atoms is associated with Daltonian atomism. I review the merits of this idea as a solution to problems posed by developments in early nineteenth century chemistry and go on to suggest that subsequent developments in chemistry are as much in agreement with ideas associated with Aristotle as with the ancient atomists, if not more so. The basic issues can be understood without getting involved in detailed chemistry and I hope what I have to say will be of interest to philosophers concerned with the metaphysics of matter but with no special knowledge of chemistry.

From a modern point of view, compounds are contrasted with elements of which they are composed, and the two categories combine to give the category of substances. Mixtures, on the other hand, might be understood to contrast with pure substances (substances in isolation), so that mixtures are quantities of matter containing several substances (be they compounds or uncombined elements) whereas pure substances are understood to be quantities of matter exhausting the material contents of a region of space which contain only one substance, and might be either a compound or an element. But heterogeneous quantities of matter (comprising several phases) might also be understood to be mixtures. Thus, it is common to speak of a mixture of ice, liquid water and water vapour in equilibrium at the triple point of water, although there is only a single substance present. The general concept of mixture as treated by Gibbs’ phase rule is a quantity of matter comprising either several substances or several phases, “or” being used in the inclusive sense. Gibbs’ phase rule is a relatively recent development in the history of the concept of chemical substance, dating from the latter half of the nineteenth century. The concepts and distinctions it presupposes have not always been apparent. I trace some of the important conceptual developments underlying the important distinctions at issue here from Aristotle, who didn’t distinguish either substance and phase, or what are now called compounds and solutions.

The Aristotelian notion of a proper mixture is that of a homogeneous body potentially separable into a definite proportion of elements. Its relation to more modern chemical ideas is not without interest despite the success of modern atomic theory. But there is a fundamental conflict entailed by Aristotle’s two approaches to the characterisation of elements, one in terms of the properties they exhibit in isolation and another in terms of their role as constituents of compounds. Although one source of problems for Aristotle has been put aside in modern chemistry, it seems that the underlying tension remains an issue.

The accumulation of knowledge concerning the character and transformations of substances from ancient times constitutes progress in chemistry, which has accelerated enormously since the end of the 17th century. The present short article focuses on some themes in the development of theorising and conceptual clarification at the macroscopic and microscopic levels during the 19th and 20th centuries. This covers the general understanding of substances in relation to phase and the general notion of a mixture, the distinction between daltonides and berthollides, and issues connected with the notion of molecular structure. Together with the enormous body of factual material accumulated particularly over the last two centuries, this is progress in chemistry. The epistemological approach seems to give the best account of it amongst philosophical views on progress currently on offer.