Chemistry and “The Theoretician’s Dilemma”

This contribution addresses Hempel’s well-known “The Theoretician’s Dilemma” from the viewpoint of philosophy of chemistry. While from the viewpoint of mainstream philosophy of science it might appear that the issues raised by this paper, published in 1958, are well settled, philosophy of chemistry has the potential to reopen the debate on theoretical terms in an interesting way. In this contribution I will reopen the debate and approach the problem of theoretical terms in a fashion which may be instructive to the wider philosophy of science. In “The Theoretician’s Dilemma” the argument hinges on the purpose of theoretical terms. Theoretical terms either serve their purpose (that is, they form part of a deductive chain that establishes definite connections between observables), or they don’t. Hempel then mounts an argument to show that if theoretical terms serve their purpose, they can be dispensed with. On the other hand, of course, if the theoretical terms don’t serve their purpose, they should be dispensed with. Hence the dilemma shows that theoretical terms are unnecessary. Hempel’s way out of the dilemma is to attack its premise. Hempel argues that theoretical terms do more than just establish a convenient shorthand to describe observations. Theoretical terms, argues Hempel, serve an ontological function in addition to theoretical systematization. Theoretical terms pick out some essential feature of nature such that they allow theories to “track truth” (in the words of Psillos 1999). From the viewpoint of philosophy of chemistry, the issue is this. Chemical theories frequently refer to entities, such as “atoms,” “chemical elements,” “electrons,” and “orbitals” that have some counterpart of the same name in theories of physics. Such chemical theories, as per the quote from Nagel above, are generally formulated with great care, as are their counterparts in physics. Yet is also the case that the use of such terms in the theories of chemistry is in many cases inconsistent with how these same terms are conceived in physics.

Contingencies in Chemical Explanation

“Chemistry has a position in the center of the sciences, bordering onto physics, which provides its theoretical foundation, on one side, and onto biology on the other, living organisms being the most complex of all chemical systems” (Malmström et al.). Thus begins a recent essay on the development of modern chemistry. Philosophers have long wrestled with how best to describe the exact relationship between chemistry and physics. Is it an example of a classic reduction? But before we ask whether chemistry could in principle be derived from physics, there is a prior question: How well integrated is the science of chemistry itself? This chapter argues that although there is a coherent explanatory core within chemical theory, contingency plays a larger role than is usually recognized. Furthermore, these phenomena at the boundaries of traditional chemistry education are where some of the most important current research is occurring. I will first adopt a quasi-historical approach in this essay, including anecdotes from my own educational trajectory. I then briefly discuss how our current understanding of the explanatory structure of chemistry should be reflected in education today. The professor of quantum chemistry at the University of Illinois in the 1950s told us a story from his PhD defense. His director, Linus Pauling, walked into the room and said something to this effect: “Well, Karplus, you’ve done a bunch of calculations on the hydrogen molecule ion (H2 +). Very nice. But you claim to be a chemist. So please write the Periodic Table on the board for us.” Who knows exactly what point Pauling was actually trying to make, but it reminds us of this basic point. The periodic table with its horizontal and vertical trends is still the basis of the classification of enormous amounts of information about the formulae and properties of chemical compounds. Mendeleev would not have understood talk of strontium-90, but he would have realized immediately that this product of nuclear testing would enter the body in a manner similar to calcium.

The Changing Views of a Philosopher of Chemistry on the Question of Reduction

The question of the reduction of chemistry to quantum mechanics has been inextricably linked with the development of the philosophy of chemistry since the field began to develop in the early 1990s. In the present chapter I would like to describe how my own views on the subject have developed over a period of roughly 30 years. A good place to begin might be the frequently cited reductionist dictum that was penned in 1929 by Paul Dirac, one of the founders of quantum mechanics. . . . The underlying laws necessary for the mathematical theory of a larger part of physics and the whole of chemistry are thus completely known, and the difficulty is only that exact applications of these laws lead to equations, which are too complicated to be soluble. (Dirac 1929) . . . These days most chemists would probably comment that Dirac had things backward. It is clear that nothing like “the whole of chemistry” has been mathematically understood. At the same time most would argue that the approximate solutions that are afforded by modern computers are so good as to overcome the fact that one cannot obtain exact or analytical solutions to the Schrödinger equation for many-electron systems. Be that as it may, Dirac’s famous quotation, coming from one of the creators of quantum mechanics, has convinced many people that chemistry has been more or less completely reduced to quantum mechanics. Another quotation of this sort (and one using more metaphorical language) comes from Walter Heitler who together with Fritz London was the first to give a quantum mechanical description of the chemical bond. . . . Let us assume for the moment that the two atomic systems ↑↑↑↑ . . . and ↓↓↓↓ . . . are always attracted in a homopolar manner. We can, then, eat Chemistry with a spoon. (Heitler 1927) . . . Philosophers of science eventually caught up with this climate of reductionism and chose to illustrate their views with the relationship with chemistry and quantum mechanics.

Philosophical Issues in (Sub)Disciplinary Contexts: The Case of Quantum Chemistry

IN A WAY, QUANTUM chemistry was “born” as a philosophical problem: It was, of course, chemistry, but owed its scientific status to physics; it was physics with the promise of explaining all of chemistry. Thankfully, following P. A. M. Dirac’s verdict (1929), this state of affairs, at least some years after 1929, was for a future world, an almost utopian world. In the meantime, chemists, physicists, and mathematicians for about half a century defying Dirac’s soothing call that all is well, but only on principle, brought about a new subdiscipline and all the methodological, epistemological, and philosophical problems that go along with the formation of any subdiscipline. In this chapter we put forward a proposal as to how we can write the history of an “in-between” discipline such as quantum chemistry, suggesting that this proposal can be extended to other “in-between” disciplines. Then, we address the role of theory in chemistry, and specifically in quantum chemistry, including the issues surrounding the ontological status of theoretical entities, and proceed to discuss the implications of the introduction of computers in quantum chemistry and the concomitant reconceptualization of experiment. Finally, we reappraise the question of reductionism from the perspective of the practitioners of quantum chemistry. From the very beginning of the period when chemical problems were examined quantum mechanically, everyone involved in the subsequent developments tried to understand the chemical character of what was begotten in the encounter(s) of chemistry with quantum mechanics. Was quantum chemistry the subdiscipline for all those chemical problems formulated in the language of physics which could be dealt with by a straightforward application of quantum mechanics with, of course, the ensuing conceptual readjustments? Was it the case that chemical problems could be dealt with only through an intricate process of appropriation of quantum mechanics by the chemists’ culture? Furthermore, the development of quantum chemistry brought about new entities whose ontological status was continuously under negotiation: exchange energy, resonance, and orbitals were some of the more intriguing entities.

How Properties Hold Together in Substances

A main aim of chemical research is to understand how the characteristic properties of specific chemical substances relate to the composition and to the structure of those materials. Such investigations assume a broad consensus regarding basic aspects of chemistry. Philosophers generally regard widespread agreement on basic principles as a remote goal, not something already achieved. They do not agree on how properties stay together in ordinary objects. Some follow John Locke [1632–1704] and maintain that properties of entities inhere in substrates. The item that this approach considers to underlie characteristics is often called “a bare particular” (Sider 2006). However, others reject this understanding and hold that substances are bundles of properties—an approach advocated by David Hume [1711–1776]. Some supporters of Hume’s theory hold that entities are collections of “tropes” (property-instances) held together in a “compresence relationship” (Simons 1994). Recently several authors have pointed out the importance of “structures” for the coherence of substances, but serious questions have been raised about those proposals. Philosophers generally use a time-independent (synchronic) approach and do not consider how chemists understand properties of chemical substances and of dynamic networks of chemical reactions. This chapter aims to clarify how current chemical understanding relates to aspects of contemporary philosophy. The first section introduces philosophical debates, the second considers properties of chemical systems, the third part deals with theories of wholes and parts, the fourth segment argues that closure grounds properties of coherences, the fifth section introduces structural realism (SR), the sixth part considers contextual emergence and concludes that dynamic structures of processes may qualify as determinants (“causes”) of specific outcomes, and the final section suggests that ordinary items are based on closure of relationships among constituents additionally determined by selection for integration into more-extensive coherences. Ruth Garrett Millikan discussed the concept of substance in philosophy: . . . Substances . . . are whatever one can learn from given only one or a few encounters, various skills or information that will apply to other encounters. . . . Further, this possibility must be grounded in some kind of natural necessity. . . . The function of a substance concept is to make possible this sort of learning and use of knowledge for a specific substance. . . . (Millikan 2000, 33)

Introduction

The Philosophy of Chemistry emerged in Europe during the 1990s—or to be more precise, in the year 1994. Since that time, the field has grown in stature and importance, offering a unique perspective on chemistry and its place within the natural sciences. For example, the International Society for the Philosophy of Chemistry (ISPC) was formally established in 1997, following some earlier gatherings among the early enthusiasts of the field, and has held meetings every year since. The journal of the society, Foundations of Chemistry, began appearing in 1999 and is now in its sixteenth year of publication, with full recognition from the Science Citation Index. But the emergence of the philosophy of chemistry has hardly been an easy process. As Joachim Schummer points out in his editorial for the journal Hyle, the other journal dedicated to the philosophy of chemistry, the philosophy of chemistry had been mostly ignored as a field, in contrast to that of physics and, later, biology. This seems to have been due to a rather conservative, and at times implicitly reductionist, philosophy of physics whose voice seemed to speak for the general philosophy of science. It has taken an enormous effort by dedicated scholars around the globe to get beyond the idea that chemistry merely provides case studies for established metaphysical and epistemological doctrines in the philosophy of physics. These efforts have resulted in both definitive declarations of the philosophy of chemistry to be an autonomous field of inquiry and a number of edited volumes and monographs. Philosophy of chemistry, like any other field of inquiry, has a historical and social context. But from a broad conceptual perspective, its birth pains seem difficult to reconcile with a rather obvious property of chemistry: Within the natural sciences, chemistry’s domain borders both physics and biology. In this regard, philosophy of chemistry is potentially unrivalled in its philosophical importance within the philosophy of natural sciences. Since it shares it boundaries with both physics and biology, no other discipline has the capacity to do more to edify the complex interactions between the life and physical sciences.

Scientific Realism and Chemistry

SCIENTIFIC REALISM Is a philosophical issue with relevance to all sciences, but there are some particularly interesting and distinctive ways in which it has manifested itself in chemistry. Paying proper attention to such aspects will deliver two types of benefits: First, it will aid the philosophical understanding of the nature of chemical knowledge; second, it will throw some fresh light on the realism debate in places where it has developed without much attention to chemical practices and chemical concepts. In the following discussion I will attempt to make a reasonably comprehensive survey of relevant literature, while also advancing some original points and viewpoints. Recall Bas van Fraassen’s now-classic formulation of the realism debate as an argument about whether we can know about unobservable entities featuring in scientific theories, and whether we should try to know about them (van Fraassen 1980). If this is how we understand realism, and if we take the long view of the history of science, chemistry is the most important science to consider in the realism debate. Until the development of atomic, nuclear, and elementary-particle physics starting in the early twentieth century, chemistry was the science in which debates about the epistemic and ontological status of unobservable theoretical entities took place with most ferocity and most relevance to practice. An interesting contrast is astronomy, in which the Copernican Revolution brought in a long and secure phase of realism about astronomical objects far out of reach of any human senses (including those that do not even register as tiny specks of light to our eyes). In contrast, the achievements of chemistry up to the early nineteenth century only deepened the sense of inaccessibility and unobservability concerning the putative fundamental entities postulated in chemical theories. Unobservability in relation to chemical theories is not only an issue about atomism, though surely the problem was clearly present with the atomistic particles imagined by a wide range of thinkers from Democritus and Leucippus of ancient times to Descartes and other early-modern mechanical philosophers.

Who’s Afraid of Supervenient Laws?

OVER THE LAST FEW decades there has been much debate in the philosophy of science over the attractiveness–and potential costs–of supervenience. As philosophers well know, supervenience burst onto the scene as the “Davidson debate” in the philosophy of mind began to raise some provocative questions over whether it was desirable to think of mental events as in some way irreducible to physical events, while still being firmly rooted in material dependence. After some initial misunderstanding over the question of whether supervenience was committing us to a sort of ontological break between the mental and the physical, it was finally settled that the autonomy one was after need not be metaphysical; an epistemological break would do just fine. After this the merits of supervenience could be clearly considered, for it allowed one to have it “both ways” in the dispute over mental states: mental explanations could be epistemically autonomous from physical ones (and thus probably not reducible to them), even while one preserved the notion of the ontological dependence of the mental on the physical (thus avoiding any embarrassing entanglements in supernatural or other spiritually based accounts of causal influence). Davidson himself, of course, never really bought into the non-reductive materialist craze that he started, preferring to champion his own idiosyncratic view of anomalous monism, which allowed the mental to continue to exist as irreducible, even while he gave it no causal or explanatory work to do. Since then Jaegwon Kim—the person who has done most to shed light on Davidson’s view and demonstrate how the concept of supervenience could recast it as a more legitimate contender among the many proposals on the merits of non-reductive materialism—has appeared to repudiate his own earlier views about explanation and now wholeheartedly endorses a type of physicalist-based account that is even more conservative than Davidson’s. In his recent work, Kim has argued not only for the elimination of any mentally based causal descriptions (or laws) of human behavior, but also seems to call into question the very idea that in pursuing scientific explanation we need to pay much attention to secondary-level descriptions.

What Was Revolutionary about the Chemical Revolution?

THE CHANGES TO CHEMICAL theory and practice that took place in late eighteenth-century France were truly revolutionary because of the radical nature of the theoretical and methodological changes that occurred, because they were deliberately so, and because that was the start of a tradition in the philosophy of chemistry. What makes the Chemical Revolution unique among scientific revolutions is that it was anticipated by both philosophers and scientists before it occurred. This meant that the chemists who effected those changes were aware of the subversive nature of their reforms and carried out the revolution in a deliberate fashion. Three major shifts in the science of chemistry coincided in late eighteenth-century France to make the Chemical Revolution the turning point in the history of chemistry: Oxygen chemistry overthrew the reigning phlogiston theory; a cadre of prominently political chemists reformed chemical terminology, providing a new system of names based on oxygen theory; and an empiricopragmatic conception of elements as simple substances replaced a waning belief in hypostatical chemical principles. This last shift (although itself gradual) ensured that the revolutionary changes in theory and nomenclature would be the last truly radical reforms chemistry would ever need. Furthermore, the Chemical Revolution was itself a revolution in the philosophy of chemistry as it forced a change in tacit assumptions about the nature of both matter and scientific knowledge. Moreover, studies of this revolution have long shaped general philosophy of science and continue to do so. Cherry-picking the history of science for examples to fit an a priori philosophical theory should be even less acceptable in philosophy of the special sciences than in other branches of philosophy. If philosophers of science are to learn from history, it should be by analyzing changes within periods that historians recognize as revolutionary and giving a philosophical account. Hence the Chemical Revolution is a crucial point for even the most minimally naturalistic philosophy of chemistry. For some time now, historians of science have understood that the chemistry practiced before the 1770s cannot be dismissed as prescientific mysticism, as was once supposed.

Robert Boyle’s Corpuscular Chemistry: Atomism before Its Time

In her important and pioneering work on Robert Boyle’s contributions to chemistry Marie Boas Hall (Boas 1958; and Hall 1965, 81–93) portrayed Boyle’s advances as being tied up with and facilitated by his adoption of the new world view, the mechanical or corpuscular philosophy, as opposed to Aristotelian or Paracelsian philosophies or world views. In recent decades such a reading has been challenged. Historians of chemistry such as Frederic L. Holmes (1989), Ursula Klein (1994, 1995, 1996) and Mi Gyung Kim (2003) have portrayed modern chemistry as emerging in the seventeenth century by way of a path closely tied to technological and experimental practice and relatively independent of overarching philosophies or world views. Such a perspective raises questions about how productive Boyle’s attempts to wed chemistry and the mechanical philosopher were as far as the emergence of modern chemistry is concerned. This is the issue I will investigate. In recent work on Boyle’s chemistry William Newman (2006) has also taken issue with what he calls the “traditional accounts,” especially that of Hall. Newman’s quarrel with the traditional accounts is the extent to which they read Boyle’s corpuscular chemistry as emerging out of the atomism of Democritus and Lucretius and its reincarnations in the hands of early mechanical philosophers such as Descartes and Gassendi, neglecting a corpuscular tradition that has its origins in Aristotle’s Meteorology. In a range of detailed and pioneering studies Newman (1991, 1996, 2001, 2006) has documented the elaboration of the latter tradition in the works of the thirteenth century author known as Geber and its passage to Boyle, especially via Daniel Sennert, a Wittenburg professor of medicine in the early seventeenth century. While Newman’s work has led to a substantial and significant re-evaluation of the sources of Boyle’s corpuscular chemistry there is a sense in which he does not break from the “traditional” view insofar as he reads the revolutionary aspects of Boyle’s chemistry in terms of a change from an Aristotelian to a mechanical matter theory.