The Philosophy of Physics Book

Kuhn's Structure of Scientific Revolutions is still, after almost sixty years, a centerpiece of controversy about what scientists do, and what they should or should not do. Scientists in particular sometimes seem to react as if what Kuhn says devalues science, making the progress of science, through revolutionary theory, less rational and less in compliance with scientific method than they believe it to be.

McAllister's book is an attempt to turn Kuhn's Structure of Scientific Revolutions on its head. While accepting the role of aesthetic factors in the evaluation of scientific theories, McAllister builds a framework for understanding revolutions within a rationalist theory of science and theory evaluation.

The core of McAllister's framework is his claim that theories are evaluated on empirical criteria and aesthetic crieteria, and on the relationship between those two sets of criteria. Empirical evaluation is as we would expect ' confirmation and disconfirmation by empirical test. Aesthetic criteria take up the greater part of the discussion. They are laid out in Chapter 3 ' as four "classes" ' form of symmetry, invocation of a model, visualizability/abstractness, and metaphysical allegiance. He also discusses simplicity as a class of aesthetic properties, although simplicity proves to be a slippery type of criterion. Actually, all those types of aesthetic criteria are interpretable ' it's important to keep in mind that they are classes of aesthetic properties, not cut and dried properties or criteria in and of themselves.

Aesthetic criteria change over time ' what models scientists accept, what symmetries they strive after (or do not), whether or not theories should lend themselves to visualization, and what metaphysical allegiances the scientific community holds. For example, the mechanistic worldview of pre-20th century physics is no longer a requirement for contemporary physics, as neither is determinism. Visualizability is likewise diminished in importance for many quantum physicists, and abstraction may be held out as a virtue.

Empirical criteria, though, do not change, according to McAllister. The test of a theory against observation is a constant.

Revolutions happen when the aesthetic criteria that characterize a scientific community's evaluations of theories ' termed the "aesthetic canon" ' become increasingly stressed and violated by theories that outperform aesthetically compliant theories on empirical grounds. Thus, despite its damage to metaphysical tenets concerning determinism, visualizability, and the mechanistic view of the universe, quantum theory's empirical superiority to classical physics carried the day. The aesthetic canon had to change in response. The revolution occurs when the aesthetic canon is overthrown in favor of a new or radically changed one.

Aesthetic factors are thus a conservative force, contrary to Kuhn, for whom it is what McAllister terms aesthetic factors that actually push revolutions forward against empirically superior established theory.

Having presented his framework, McAllister then analyzes two sets of case studies in its light. One is the pair of candidate astronomical revolutions ' Copernicus's heliocentric theory and Kepler's theory of elliptical orbits ' and the other is the pair of 20th century landmarks in physics ' relativity theory and quantum theory.

McAllister's analysis leads him to claim that relativity theory and Copernican theory were not true revolutions. Neither, in his view, constituted an overthrow of existing aesthetic criteria for theory evaluation. Copernican theory, for example, retained from traditional, Aristotelian theory, requirements of circular and uniform motion for celestial bodies, even re-affirming those principles against Ptolemy's use of the equant point to anchor the orbits of those bodies. Kepler, by contrast, abandoned circular and uniform motion in his theory of elliptical orbits.

He also claims that Copernican theory and relativity did not constitute the kind of stress on aesthetic criteria by virtue of empirical superiority that he believes characterizes true revolutions. Again, in the case of Copernican theory, it's famously not clear that Copernican theory outperformed Ptolemaic in terms of predicting the positions of objects in the sky. It fails to fit the framework McAllister has argued for.

As against Kuhn, McAllister is claiming that the roles of aesthetic criteria and empirical criteria are reversed. In revolutionary science, empirical superiority stresses accepted aesthetic criteria to the breaking point, rather than Kuhn's less rationalistic model, in which aesthetic criteria take the lead.

What is called "normal science" for Kuhn, is for McAllister a period of time in which both empirical and aesthetic criteria remain in place, as McAllister claims was the case during the Copernican period. Revolutions happen when theories' empirical performance outpace the scientific community's adherence to a current aesthetic canon.

McAllister develops his framework primarily through analytical means, using thoughts and anecdotes from the practices of scientists more to illustrate points than to inspire his theory. In the case studies, he then holds the resulting framework up against scientific practices during real and supposed revolutionary times, to confirm his theory.

But the order in which he develops his framework is from the analytical and abstract to the test against facts, now interpreted within the framework itself. He doesn't motivate the framework by showing inadequacies in Kuhnian thinking for accounting for the facts ' the facts about scientific practices instead come after the framework.

He also uses his theory to interpret those scientific practices. For example, enlightened by his theoretical framework, Copernican theory fails to be a true revolution.

If we were trying to understand why Copernican theory was not a revolution, that's great. But if we are determining whether or not it was a revolution, where that is still an open question, I think that McAllister's arguments aren't quite so strong.

A different story could be told, emphasizing Copernicus's rejection of geocentrism (and other metaphysical principles of the Ptolemaic universe), rather than the conservation of circular and uniform motion, and claiming that in fact, it was this rejection that carried the day in spite of the theory's lack of empirical superiority.

Further, what counts as a "revolution" in science is certainly debatable. There's no fact of the matter about that ' it's a judgment, I think, far more than a fact. Thus a theory of scientific revolution that explains that one instance ' the Copernican ' was not really a revolution and another ' the Keplerian ' was, can't really be said to be thereby "confirmed." It is hard to say that the theory is "true" when its confirmation follows from facts being viewed through its lens rather than in some way neutrally.

The theory may of course still be "enlightening" as a coherent interpretation, and I think McAllister's is enlightening within the large mix of thinking about what scientists do.

I will mention one potential advantage of Kuhn's framework that I think is important. In a Kuhnian world, scientific revolutions may not be entirely autonomous within science ' political, artistic, philosophical, . . . all sorts of factors may influence aesthetic criteria independently of anything contained within science itself and become important factors in fomenting revolution. For McAliister, certainly there can be such extra-scientific factors at work in helping revolutions along, but the driving force for him is superior empirical validation of new theories.

Reading McAllister's theory of revolution, and contrasting it with Kuhn's, raises, to me anyway, an overarching question: What is the purpose of a theory of scientific revolutions (or of a theory of scientific practice in general)? Is it to better understand what scientists do, or is it to prescribe how science ought to be done, or both?

I'm not sure that McAllister wants to change anything that scientists do, or even influence them to think about what they do differently. Kuhn, I'm not sure of. He certainly has upset a lot of scientists, especially with his more radical claims about incommensurability and discontinuity in science.

I think it is also interesting to contrast both McAllister and Kuhn with Feyerabend on this question ' I don't think that Feyerabend, despite his reputation as a radical thinker, wants to change what scientists do, so much as prevent them (or philosophers of science) from constraining what they do with a theory of what they do.

I'll stop there. I think I just opened a big can of worms.