Just what is chemical philosophy?

Eric R. Scerri (2008) Collected Papers on Philosophy of Chemistry. Imperial College Press, London. ISBN-13 978-1-84816-137-5: ISBN-10 1-84816-137-9: 248 pages. Price: $101 / 56.

Reviewed by: Joseph E. Earley, Department of Chemistry, Georgetown University, Washington, DC, USA.

What has philosophy to do with chemistry? Robert Boyle (1627-1691) a founder of modern chemistry had a low opinion of many philosophers. He claimed that the School-philosophers have their recourse to Agents that are not onely [sic] invisible, but inconceivable. Present-day chemists frequently form similar opinions on reading philosophical discussions of possible worlds in which water is XYZ or where items display the color grue. (X is grue if X is green and was examined before time t or blue and was not examined before t.)

Recently some British philosophers attacked many of their well-recognized colleagues (analytical metaphysicians) as neo-scholastics and accused them of being practitioners of the philosophy of A-level chemistry. This taunt does not suggest that secondary-school and elementary-level university chemistry courses (roughly corresponding to the British A-level), or degree programs from various schools do not connect with significant conceptual issues, but rather it claims that adequately dealing with present philosophical problems requires real acquaintance with current work in advanced contemporary science adequate familiarity that cannot be gained merely from elementary-level instruction, or by means of thumbing indexes of beginners textbooks.

Collected Papers on Philosophy of Chemistry contains a generous sampling of the work of Eric Scerri, a chemist, historian and philosopher of science who brings a mature grasp of relevant current science to bear on the important philosophical problems that intersect elementary chemistry instruction. He does not engage in elaborate flights of philosophical fancy such as those that working chemists (and many others) find at best unconvincing, but rather he brings sound chemical, historical, and philosophic scholarship to bear on the many aspects of chemical teaching that concern long-standing philosophical puzzles. Such work illuminates chemical education in interesting and unexpected ways, and also may well contribute to resolving problems in academic philosophy that have resisted other approaches. The main topic of first part of the body of the book is whether or not chemistry has been reduced to physics, as physicist Paul Dirac (1902-1984) famously claimed or, if not, whether such reduction is possible. The obverse of this issue is the question of whether (or to what extent) truly novel coherences can properly be considered to arise ( emerge ) from simpler components. (These discussions are clearly relevant to whether chemistry should be recognized an autonomous science, rather than considered a mere off-shore colony of physics.)

The second main section of the book deals with the periodic table of the elements. Papers in this section provide the basis of parts of the author s well-received recent book The periodic table: its story and its significance, (NY: Oxford University Press, 2007). Scerri argues that much of the success of the work of Dmitri Mendeleev (1834-1907) was due to his use of a concept of chemical element that was rather different from that used by other nineteenth-century chemists. As Scerri points out (page 127) For Aristotle, the elements are themselves unobservable. the elements are immaterial qualities impressed on an otherwise undifferentiated primordial matter and are [all] present in all substances. Like this ancient concept, Renaissance and early-modern notions of elements those of Paracelsus (1493 1541) or Boyle, for instance were all more or less metaphysical. (The ancient element water was not the concrete liquid we all know and use. The Paracelsian principle sulfur was not the same as the yellow powder in the apothecary s jar.) Scerri claims that: this view was first seriously challenged by Lavoisier during the course of the chemical revolution. Antoine-Laurent de Lavoisier (1743 1794) identified certain concrete kinds of tangible stuff as elements properly so called. Specific kinds of solids, liquids, and gases yellow solid sulfur, metallic liquid mercury, and pungent gaseous chlorine all merited the designation element. In the 1920s, Austrian-born chemist Friedrich (Fritz) Paneth (1887- 1958) pointed out that Mendeleev had employed a more complicated notion of elementarity than was usual in the century that followed Lavoisier s death. Paneth pointed out that the Russian chemist had used two quite different meanings of the term element depending on the circumstances. One the one hand, he construed the word element to denote concrete materials (solid sodium metal and gaseous dichlorine, for example) and, on the other hand, he interpreted the same word to refer to each of the several chemically ultimate constituents of specific compounds the sodium and chlorine in common salt, for instance. Paneth noted that this second meaning was quite different from the first meaning and also that is was just as metaphysical as Aristotle s concept of element had been. Contemporary chemists routinely follow Mendeleev s example and use a two-fold concept of element but generally they do so automatically and quite unconsciously. Chemistry instructors expect students to understand that the sodium that is a component of common salt is not a soft metal, and that chlorine (as a component) is not a pungent gas but they generally do not call attention to fact that they commonly use each of the terms element, sodium and chlorine with two quite distinct meanings. It seems likely that they themselves do not recognize this double-speak (more politely, polysemy or ambiguity ). Scerri usually designates one-component stable materials as simple substances and uses the term basic substance to refer to chemically-ultimate components of compounds. Elsewhere I have suggested that elementary substance instead of simple substance be used to stand for one-component stable materials (Lavoisier s elements ) and that the word element be reserved to designate components of compounds what Scerri calls basic substances. This minor shift in word usage would remove serious but unnecessary difficulties for English-speaking chemistry students.

The second section of the book also deals with aspects of quantum chemistry that pertain to whether or not the periodic law so important to chemistry has been (or could be) deduced from quantum physics. From the exact solution of the Schrödinger equation for the hydrogen atom one can reasonably infer the maximum population of each electron-shell and electron-sub-shell in multi-electron atoms but all known methods of prediction of the order of filling of sub-shells (the basis of the periodic law) require that empirical data be fed by hand into approximate computations. The degree to which chemical periodicity can be inferred from quantum physics is arguably much less than has widely been supposed (and claimed). The third section of the book contains papers that inter-connect the main themes of the earlier parts of the book and relate them to principal problems of science education and of recent philosophy of science. Several papers conclude that chemists generally adopt an intermediate attitude between naïve realism on the one hand and anti-realistic empiricism on the other hand. Scerri notes that philosophers of science have moved away from normative approaches that concerned how science should be done toward more naturalistic attitudes which deal with how science actually is (or has been) done. In the last chapter the author points out something that perceptive readers may have already noticed that his thinking has shifted and significantly developed over the period covered by this book. For instance, for the past half-century chemists have effectively interpreted their experimental results in terms of atomic and molecular orbitals even though quantum physics clearly teaches that such orbitals do not exist. for the multiple-electron systems with which chemists deal. For some years Dr. Scerri advised chemists to repent their errors and mend their ways a normative counsel. More recently he has come to a more complex ( naturalistic ) view. He reports:

The thought came to me that it is quite appropriate for chemists and chemical educators to not only use orbitals but to do so in a realistic fashion in spite of their status according to the fundamental theory of quantum mechanics. I fully realized at this moment the truly paradoxical situation that chemistry is an autonomous science while at the same time resting on fundamental physics. (Page 218)

This paradoxical situation of chemistry may account for the fact that, as the back cover of the book claims, the Philosophy of Chemistry is one of the newest and fastest-growing areas in the Philosophy of Science. General readers (or chemists, science educators, or philosophers) seeking an overview of this area could find no more effective, concise, convenient entry into this important and actively developing field than the one that this volume provides.

1 Ladyman, James and Ross, Don (2007). Every Thing Must Go: Metaphysics Naturalized. Oxford: Oxford University Press. Section 1.2, especially page 24.

2 Earley. Joseph, (2009). How Chemistry Shifts Horizons: Element, Substance, and the Essential, Foundations of Chemistry, Volume 11, pages 65-77.