This book is the apologia of a frustrated reductionist. The frustration derives from Rosenberg's clear perception that the project of physicalist reduction, the reduction of all the sciences of complex objects to physics, is impossible, at least, as he often says, for beings hampered by our limited cognitive and computational abilities. The reductionism that survives this realisation is purely metaphysical. It is the firm commitment to the view that ultimately whatever happens happens because of the universally lawlike behavior of the physical particles of which everything is composed. What holds these theses together is supervenience. The physical correlate of a higher level property or kind is typically massively disjunctive. Thus although the intrinsic properties of a complex thing are fully determined by the properties of the physical particles of which they are composed, the physical property necessary and sufficient to determine such a higher level property is too complex and disjunctive for our feeble minds to grasp. The underlying physical heterogeneity of the properties or kinds we distinguish at higher structural levels is such as to make it vanishingly unlikely that these will enter into the kinds of universal laws characteristic of physics or chemistry.
Rosenberg has an explanation for this sorry state of afairs: complex objects in biology, at least, came into being through natural selection. And selection sees only function and is blind to structure. Thus selection has produced properties and kinds that are functionally homogeneous but structurally diverse. And being structurally diverse, they will be more or less unreliable in their behavior. Therefore biological kinds and properties cannot be natural kinds in the sense that physical and chemical kinds are, and biology should be viewd at best as instrumentally useful rather than realistic.
Somewhat surprisingly, Rosenberg does think that a sufficiently abstract version of evolutionary theory is nevertheless universally true in just the sense that the laws of physics are. The problem is that in the sense it is true it is largely inapplicable to cognitively empoverished beings such as us. Following Mary Williams proposed axiomatization of evolutionary theory, Rosenberg endorses the idea that every organism has some "positive real number that describes its fitness in a particular environment." This number, however, supervenes on a host of genetic particularities of the organism, and we have no chance of identifying a class of sufficiently similar organisms to which it applies even holding constant the continuous flux of environmental change. Thus this law, while expressing the objective reality of natural selection, is at best of heuristic value in application to the study of real evolutionary processes.
Rosenberg harbors no doubts about the universal reign of law at the microphysical level. No doubt he shares this assumption with many other philosophers. Nevertheless it would have been nice to see a bit more argument for this view. The only such argument I could find was the claim that the predictive accuracy of physics and chemistry "had persistently increased in range and depth over the last four hundred years" (p. 36). No doubt this is true, though as Rosenberg adds in a footnote Newtonian mechanics has reached a severe obstacle with the three-body problem (a problem attributed to our limited computational powers) and chaos theory shows that even universal determinism cannot guarantee predictive improvement. The trouble with all this is that whatever are our grounds for believing that the laws of physics and chemistry apply uniformly everywhere, they are not empirical. Only in quite special and very carefully controlled circumstances are they predictively accurate, however impressively so. It is true that we express our knowledge of the laws of physics in universal form, but the assumption that they apply in all the increasingly complex circumstances far beyond our computational capacities to verify requires a vast inductive leap of faith. It is striking, in this connection, that Rosenberg seems to take this kind of imperialistic physicalism to be intricately connected with empiricism (p. 10). No doubt another ground for Rosenberg's view is his assumption that the macroscopic world is fully deterministic, as quantum indeterminacy becomes increasingly insignificant and "nature ... has long since asymptotically approached determinism' (p.61). This, again, can be no more than an act of faith in view of Rosenberg's continued insistence that we can never expect to discover the deterministic laws governing macroscopic behavior. (I cannot pass up the opportunity of protesting the quite inexplicable attribution to myself of concurrence with this claim of macroscopic determinism [p.61n]).
In two concluding chapters Rosenberg extends his arguments to the human and social sciences. Here the outlook is considerably more pessimistic than for biology. For the human mind not only carries all the problems of being a biological phenomenon, but adds a whole level of complexity through the phenomenon of intentionality. The psychological, thus, is doubly supervenient: it supervenes on neurophysiology, which itself supervenes on the physical. The analysis, whatever one thinks of the metaphysics, is plausibly deployed against the more scientistic pretensions of some parts of psychology and social science.
In reading this book, I found myself agreeing with many of the premises but disagreeing with most of the conclusions. Where Rosenberg sees limitations to biological knowledge as revealing its instrumental character, I see arguments against the empirical tenability of the mechanistic metaphysics Rosneberg assumes. Nevertheless, it does seem to me that Rosenberg draws attention to many of the fundamental issues in understanding contemporary biology, and he faces with unusual honesty the difficulty of sustaining mechanism in the light of current biological knowledge. I found the book stimulating to read. Rosenberg generally has interesting arguments for the claims he makes, and with occasional exceptions (as that noted above) treats the authors he argues against carefully and fairly. The book makes an important contribution to the central debates in philosophy of biology.
JOHN DUPRÉ
Stanford University