Scientific inference, part 4 of 4

April 3, 2009 at 10:24 am

Having gone over Popper’s readiness to reject theory, and Quine’s readiness to reject data (kind of), let’s get to the Goldilocks of scientific epistemology, Thomas Kuhn. Kuhn was not trained as a philosopher but as a physicist when he started teaching a course on the history of science at Harvard and as such his work is mostly descriptive whereas Popper and Quine are prescriptive. In teaching this course he developed the ideas that he eventually published as The Structure of Scientific Revolutions. While the term “paradigm shift” is what most people remember about this book — and which became fashionable among business types in the 1990s — the real interest is what happens within the paradigms.

A paradigm is a more or less cohesive agenda and set of guiding principles. The paradigm thus shows scientists what sort of questions to ask and what are reasonable ways to go about answering them. Kuhn refers to work within a paradigm as “normal science” which mostly consists of “puzzle-solving.” Contra Popper, normal science consists of working out minor puzzles about exactly how the paradigm works, but not if the paradigm works as this is taken for granted. This is holism in practice in both a positive and negative sense. In the positive sense, the paradigm provides coherence to the universe and presents manageable chunks of reality for the scientist to chew on. As anticipated by Duhem, one of the things the paradigm does is tell the scientist what a meaningful problem looks like. (Note that this implies that the “grounded theory” method is not very Kuhnian). In the negative sense, the paradigm can blind the scientist to evidence against it for when observations contradict the theory they are impossible to interpret and must be shunted off to some auxiliary hypothesis.

Whenever evidence contradicts predictions of the paradigm this does not cause the rejection of theory but merely presents “anomalies.” These anomalies can be temporarily accommodated by speculation about measurement error or epiphenomenal forces. Eventually though such perturbations in the web of belief make it so convoluted as to be less than useful. At this point a scientist or small circle of scientists creates a new paradigm which can accommodate the anomalies. Unlike the cruft-besotten old paradigm, the new paradigm is internally consistent, but it is also fairly vague and may lack details as to exactly how the paradigm work. Fleshing out these details thus becomes puzzle-solving for a new generation of normal science and we come full circle.

I choose the engineering metaphor “kruft” advisedly. Think of a newly created paradigm as like version 1.0 of a computer operating system. Over time the OS encounters problems and people create often clumsy solutions to work around these problems. Eventually these solutions clutter the original elegance of the system and create kruft. Then you have a choice, you can stick with it or you can create something from scratch. The new thing will be more elegant but it won’t have worked out lots of specific problems, say, device drivers. So switching to the new OS is cleaner, but is not fully fleshed out enough to deal with the messiness of reality. Switching from Windows to Linux is going to improve your memory allocation since it’s actually designed for a powerful computer, not jerry-rigged out of something designed for a 386, but it’s also going to be harder to get your application software and your monitor to behave with the OS. The same is true of a new paradigm, it’s going to solve many of the old anomalies but it’s also not going to say much concretely about a lot of empirical problems.

Thus, Kuhn essentially took holism and ran with it, but added a somewhat Popperian element during unsettled periods. It is especially worth noting that Victorian scientists had identified numerous anomalies in the Newtonian paradigm which Einsten was able to solve with the general relativity paradigm. Thus Kuhn’s model of science is a very good description of the positivists’ favorite case of good science.

Combining holism and positivism is something of a Goldilocks problem. If Popper wants us to be ready to discount theory and Quine wants us to be ready to discount data, Kuhn finds a way that they can both be right. Most of the time his model resembles holism, but when the web becomes too knotted by accommodating anomalies it shatters and we get a paradigm shift somewhat like Popper’s falsification.

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