Perspectives on Science 7.3 (1999) 337-348
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Unification as a Regulative Ideal * - [PDF]
Symposium: The Disunity of Science
The Unity of Science Movement is dead. If philosophers ever believed that science could be organized as a hierarchy of theories founded on general principles with the basic generalizations of "higher level" theories derivable from those of more "fundamental" theories, then they do so no more. The doctrine that chemistry is reducible to physics, biology to physics and chemistry, psychology to biology, and the social sciences to psychology has suffered from scrutiny of crucial junctions--particularly those between biology and the physical sciences, and between psychology and biology. The following points are, I hope, relatively uncontroversial. (1) Some sciences, particularly parts of biology, psychology, and the social sciences, are not happily viewed as collections of laws that can be organized in an axiomatic system. (2) Some sciences legitimately employ functional concepts (like the concept of a gene) and historical concepts (like many taxonomic concepts) that resist identification in structural terms. (3) Even to the extent that some "higher-level" sciences contain generalizations whose component concepts can be specified in terms of the concepts of "lower-level" sciences, the derivation of these generalizations from the specifications and the principles of the "lower-level" sciences would not be explanatory. We wouldn't deepen our understanding of Mendelian rules of inheritance by deriving them within molecular cell biology, even if we could give the derivation.
The questions raised by this symposium center on how far we want to depart from the picture of one science, hierarchically organized. Some philosophers, Ian Hacking, John Dupré, and Nancy Cartwright, have [End Page 337] argued for radical changes. At risk of blurring important distinctions among their views, we can see them as contending that the world is diverse and disorderly and that, correspondingly, the sciences are many and particular. In her probing analyses of the role of laws in parts of physics, Cartwright has suggested that traditional images of the structure of science break down even within fields, and she has emphasized the piecemeal, even gerrymandered, character of physical research.
My own reaction is different. Rather than abandoning the ideal of unification, I've suggested that the Unity of Science Movement understood it in the wrong way. Consider fields of science as defined by the questions they seek to address, often questions that are organized in complex tree-like structures. Pick up any copy of Science or Nature, and you will find article after article with titles like "Evolution of the Pacific-Antarctic Ridge South of the Udintsev Fracture Zone," "Lung Structure and Ventilation in Theropod Dinosaurs and Early Birds," and "Nonsyndromic Deafness DFNA1 Association with Mutation of a Human Homolog of the Drosophila Gene diaphanous" (all from Science November 14, 1997). Why, you might ask, are these projects of such interest that they deserve publication in one of the world's two major general science journals? Well, these quite particular discoveries offer a way forward on investigations that the cognoscenti see as particularly interesting: if you want to know how major geological features are produced, you need to understand interactions among plates, and, since one of the important interactions involves axial rotations you need to look at those, and, since a particular ridge in the South Pacific is a good case to study, data about that ridge are significant; if you want to understand the history of life, you need to study the large transitions, of which the reptile-bird transition is a good example, and, since the lungs of modern birds modify those of reptiles in ways that allow endothermy, data about the lung structures of late dinosaurs and early birds make a significant contribution to the larger project; in the last example, there are links both to the theoretical project of understanding comparative physiology and development, and to practical projects of tackling human diseases; I'll return to this mix of the theoretical and the practical later.
Workers in any field know how their projects relate to those of their colleagues, and, typically, see their own...