Science is a reductionist enterprise. It is no coincidence that Thales of Milete, the natural philosopher from ancient Greece who argued that everything is composed of water, is often regarded as the first scientist. Thales was a reductionist pur sang because he tried to reduce the complex world to one simple, fundamental principle. Reductionism is the doctrine that complex phenomena at a 'higher' level can be fully explained by simple phenomena at a 'lower' level. The reductionist claims that, for example, the formation and behaviour of mountains, rivers, living organisms, and even societies, are to be studied by analyzing the parts of which these phenomena consist (in the last instance, elementary particles). Accordingly, reductionism assumes that all phenomena are in principle explicable by appeal to fundamental physical laws. The implication for the geosciences is that reconstructions of the geological past and explanations of earth-scientific phenomena can ultimately be reduced to laws that describe the behaviour of the fundamental constituents of matter.
Since Thales, science has been extraordinarily successful, and most of its successes were the result of methods that reflect a reductionist attitude: scientists typically try to gain knowledge of and insight in the world around them by means of analysis and simplification. For example, in the 17th century Newtonian mechanics provided reductive explanations of many complex phenomena, such as the motions of the planets and the tides. In the 19th century, Maxwell unified the phenomena of electricity, magnetism and light by reducing them to manifestations of an underlying electromagnetic field. Moreover, kinetic theory reductively explained the laws of gases. In the 20th century, chemical laws and the periodic table were reduced to quantum theory, and biology witnessed a wave of reductions by molecular biology and genetics. Today, elementary particle physicists are hunting for the 'Theory of Everything', which would explain all natural phenomena, at least in principle, on the basis of a single fundamental law of nature. Incidentally, the question of whether everything can be reducd to physics is not merely an academic debate: in 1993 physicist Steven Weinberg defended reductionism in the American Congress in order to support the construction of the Superconducting Super Collider, a giant particle accelerator that would cost billions of dollars (despite his plea, it was not built).
In the 1930s philosophy of science came of age, and philosophers of science, being deeply impressed by scientific successes, wanted to establish a solid philosophical foundation for science. Their aims were reductionist in spirit. This so-called logical-positivist movement defended the idea of Einheitswissenschaft (unified science): all sciences share a single language and a single method, based on empirical observation and induction. Scientific disciplines are thereby unified in the form of a reductive hierarchy, in which the higher-level sciences are ultimately reducible to fundamental physics. This reductionist view was further developed in the 1950s by the philosophers Hilary Putnam and Paul Oppenheim, and Ernest Nagel. They developed a formal scheme for the reduction of theories and laws.
Reductionism was subsequently criticized by others, who argued that it faced many problems, not least the fact that in most cases from scientific practice a reduction according to the formal scheme turned out not to be possible at all, contrary to what the reductionists claimed. Reductionists replied by giving a weaker formulation of the reductive relation, the so-called supervenience relation. Today there is still a lively debate among philosophers as well as scientists about the viability of reductionism (where the reductionist stance is more popular among scientists than among philosophers). In my presentation I will give an overview of the debate about reductionism in the philosophy of science and in physics itself, and I will defend the reductionist position.
Suggested reading
Robert Batterman, 'Intertheory Relations in Physics', in: Edward N. Zalta (ed.) Stanford Encyclopedia of Philosophy
Robert Klee, Introduction to the Philosophy of Science (Oxford, 1997). Chapter 5 contains an in-depth discussion of the philosophical debate about reductionism.
Robert Klee (ed.), Scientific Inquiry - Readings in the Philosophy of Science (Oxford, 1999). Section 3 contains classic papers and a useful introduction to the debate.
W.H. Newton-Smith (ed.), A Companion to the Philosophy of Science (Oxford, 2000). Contains lemmas about relevant themes: reductionism, unity of science, supervenience, etc.
Steven Weinberg, Dreams of a Final Theory (New York, 1992). An accessible and entertaining discussion of the quest for a theory of everything and a vigorous defence of reductionism by a Nobel-prize-winning elementary particle physicist.