Paul Needham

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.

Chemistry, the science of substances and their transformations with roots in antiquity, provides as rich a source as any of the claims about what is not directly observable in the light of ideas reflecting both constancy and change. An important distinction in chemistry is that between macroscopic and microscopic realms, mistaken by positivists as a distinction between observable and theoretical and later by certain realists as a distinction between the merely superficial and the deeply theoretical. Recent realist themes about the preservation of the extension of substance predicates typified by “water” and the view that 20th century scientific atomism vindicates earlier philosophical speculations about the corpuscular constitution of matter are unjustified. The relation between quantum and general chemistry is vexed. Despite questioning particular realist theses, however, none of this raises doubts about the basic realist stance that science seeks and sometimes achieves knowledge of a world independent of our thoughts.

Chemistry builds on distinctions of substance, which presupposes that matter can be divided into substances and compared with other matter and itself on different occasions as being of the same substance. Even identifying a quantity of matter as comprising a single substance presupposes the same substance relation, it being a quantity all of whose spatial parts are the same substance. But criteria of purity have been important for isolating substances and investigating their characteristic properties, which can in turn be used for establishing sameness of substance. With the development of chemistry into a theoretical science it became important that such criteria and characteristics should have a systematic theoretical basis. Thermodynamics was, perhaps, the first comprehensive theory to systematically divide the mass of the bodies with which it deals into distinct substances and offer general criteria governing the number of substances present. But the applicability of such macroscopic criteria is restricted to equilibrium conditions on a macroscopic time scale. They can be compared with microscopic conceptions of molecular structure, with which they have been complemented—some would say superseded. Since many substances are not molecular, however, the general formulation of a microscopic sameness of substance criterion remains unclear.

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.

Chemistry is the study of the structure and transformation of matter. When Aristotle founded the field in the 4th century BCE, his conceptual grasp of the nature of matter was tailored to accommodate a relatively simple range of observable phenomena. In the 21st century, chemistry has become the largest scientific discipline, producing over half a million publications a year ranging from direct empirical investigations to substantial theoretical work. However, the specialized interest in the conceptual issues arising in chemistry, hereafter Philosophy of Chemistry, is a relatively recent addition to philosophy of science. Philosophy of chemistry has two major parts. In the first, conceptual issues arising within chemistry are carefully articulated and analyzed. Such questions which are internal to chemistry include the nature of substance, atomism, the chemical bond, and synthesis. In the second, traditional topics in philosophy of science such as realism, reduction, explanation, confirmation, and modeling are taken up within the context of chemistry.

During the 19th century atomism was a controversial issue in chemistry. It is an oversimplification to dismiss the critics' arguments as all falling under the general positivist view that what can't be seen can't be. The more interesting lines of argument either questioned whether any coherent notion of an atom had ever been formulated or questioned whether atoms were ever really given any explanatory role. At what point, and for what reasons, did atomistic hypotheses begin to explain anything in chemistry? It is argued that 19th-century atomic accounts of constant proportions and isomerism had little to offer, whereas a non-atomic explanation of chemical combination was developed. Not until the turn of the century did atomism begin to do serious explanatory work in chemistry.

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

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.

A view of individuals as constituted of quantities of matter, both understood as continuants enduring over time, is elaborated in some detail. Constitution is a three-place relation which can't be collapsed to identity because of the place-holder for a time and because individuals and quantities of matter have such a radically different character. Individuals are transient entities with limited lifetimes, whereas quantities are permanent existents undergoing change in physical and chemical properties from time to time. Coincidence, considered as a matter of occupying the same place, is developed, alongside sameness of constitutive matter, as a criterion of identity for individuals. Quantities satisfy the mereological criterion of identity, applicable to entities subject to mereological relations and operations such as regions of space and intervals of time. A time-dependent analogue of mereological parthood is defined for individuals, in terms of which analogues of the other mereological relations can be defined. But it is argued that there is no analogue of the mereological operation of summation for individuals

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 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.

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.

In a recent critique of the doctrine of emergentism championed by its classic advocates up to C. D. Broad, Jaegwon Kim (Philosophical Studies 63:31–47, 1999) challenges their view about its applicability to the sciences and proposes a new account of how the opposing notion of reduction should be understood. Kim is critical of the classic conception advanced by Nagel and uses his new account in his criticism of emergentism. I question his claims about the successful reduction achieved in the sciences and argue that his new account has not improved on Nagel’s and that the critique of emergentism he bases on it is question-begging in important respects.

The creators of equilibrium and irreversible thermodynamics developed a conception of processes which bears on metaphysical discussions of change, occurrents, and continuants and merits the attention of contemporary analytic metaphysicians. It concerns the macroscopic domain, from which metaphysicians normally take their examples, and is unjustly ignored on the grounds that it is not ‘fundamental science’. Why this often-voiced view should disqualify just thermodynamics, and not the broad range of considerations normally raised, is a moot point. But even if there were an adequate reductive argument, that wouldn’t eliminate the ontological claims. It is argued that processes cannot be defined as changes in the state of enduring objects, but should be considered autonomous entities. The relational character of processes involving several continuants is developed, alongside their mereological features and their relation to space and time. Some aspects of the historical development of the notions of reversible and irreversible processes in thermodynamics are taken up in the course of the discussion, but the paper is not concerned with the mathematical foundations of equilibrium and irreversible thermodynamics. 1 Introduction2 Change3 Distinguishing Processes from States4 Causings5 The Relational Character and Mereological Structure of Processes6 Concluding Comments