Book review: The Knowledge Machine by Michael Strevens

Last spring I read and discussed Michael Strevens’ The Knowledge Machine: How Irrationality Created Modern Science with my lab group. Here’s my review.

tl;dr: a scientist who wants to dip a toe into philosophy of science could do much worse than to start with this book.

This is an unusual book in terms of both subject matter and approach.

In terms of subject matter, Strevens sets out to answer two big questions. First is a philosophical question: what distinguishes science from other human activities, such as pseudoscience or history or art or philosophy or religion or etc.? Second is a historical question: why did the activity we now recognize as science not emerge until the 17th century, in Europe? The subject matter is unusual because it’s unfashionable, even contrarian. Much recent philosophy of science, and history of science, argues that nothing distinguishes science from non-science. That there’s no clear bright line to be drawn between science and non-science, either in (philosophical) principle or in (historical) practice. And if there’s no clear bright line between science and non-science, then there can’t possibly be any Scientific Revolution–a more-or-less sudden invention of science, the date of which cries out for historical explanation.

In terms of approach, the book is unusual because it’s a popular book. If it’s not the first popular treatment of philosophy of science, it must surely be among the few. Further, it’s not a popular review of philosophy of science. Strevens does review some previous work in philosophy of science (primarily Popper and Kuhn), but only in order to set the stage for his own original answers to the two questions listed above. As best I can tell from Strevens’ cv, this book isn’t even a popular summary of his own papers. Rather, he seems to have written a popular book when most others in his shoes would’ve written a specialized scholarly monograph.

What I liked about the book:

• A very effective baby-werewolf-silver bullet structure. I suspect that a lot of scientists and science students will instinctively think it’s pretty obvious what distinguishes science from non-science. Strevens does a great job of using historical examples to undermine those instincts. He’s quite convincing that there is something distinctive about science, and that we have yet to figure out exactly what it is. Strevens also is quite good at granting every point of the most vocal critics of science (that individual scientists are inevitably biased and subjective, etc.), while still arguing that science works.
• A clear, interesting answer to his first question. According to Strevens, what distinguishes science from other ways of knowing, and makes it more effective than other ways of knowing, is that science alone follows what he terms the “iron rule”: all disputes are to be settled by empirical data. So if there are different competing scientific claims, well, figure out what experiment or other data would distinguish between those claims, and do whatever it takes to collect those data. Strevens doesn’t think there’s anything universal to be said about exactly how data can be used to settle disputes. In this, he disagrees with Popper and others. It’s not that, say, data always settles disputes via Popperian hypothetico-deductive arguments. And Strevens acknowledges that scientists always bring their own personal subjective biases to the table (while also emphasizing that they should try not to, and that science has professional practices that tamp down those biases). But he thinks that, in the long run, science will make cumulative progress towards the truth as long as scientists do their best to follow the iron rule. Strevens is quite good at emphasizing how counterintuitive the iron rule is. In particular, the iron rules says that scientists can’t appeal to other criteria when deciding among competing scientific claims. That might seem pretty obvious to us today, if the other criteria you have in mind are things like “the Bible” or “the authority of the Pope” or “seances” or whatever. But scientists who are following the iron rule also can’t favor one claim over another on grounds of, say, “parsimony”, or “mathematical rigor”, or “theoretical elegance”, or etc. It’s not at all obvious that appealing only to empirical data really is the best way to settle scientific disputes.
• Following on from the previous bullet: I found myself thinking about an analogy between the iron rule, and arguments for the efficacy of evolution by natural selection. Arch-selectionists acknowledge the operation of evolutionary forces like genetic drift and migration, that can interfere with the operation of selection. But nevertheless (so the argument goes), selection is a distinctive evolutionary force: it’s the only one that has a tendency to push populations “uphill” on the “adaptive landscape”. So that, even if selection is weak or intermittent, and even if other evolutionary forces are at work, it’s still the case that populations under selection will tend to adapt (in the long run, on average), and that populations not under selection will not. I think Strevens’ “iron rule” is a bit like natural selection. It imparts a cumulative, directional tendency towards truth onto scientific research. Even if the iron rule is only imperfectly obeyed by practicing scientists, even if the relevant data often are difficult to collect, etc. Progress towards the truth might be slow in particular cases, it might even temporarily go into reverse sometimes. But in the long run, on average, science makes progress. In contrast, fields like philosophy or literary criticism or theology don’t obey the iron rule, and so there’s no force nudging those fields towards the truth.
• Strevens illustrates his points with great historical examples, conveyed in a very readable style. In all seriousness, it’s a page turner. Now, they’re mostly canonical examples in philosophy of science, so they might be familiar to some of you. And it’s fair to wonder if it might be a bit misleading to focus on those examples, because the same features that made them canonical might also make them atypical (more on this below). But the audience for this book is people new to history and philosophy of science. For them, these examples are going to be totally eye-opening and captivating.
• Strevens has provocative thoughts about how to organize scientific practice, and what values and behaviors to instill in individual scientists. At least, I think they’ll be provocative to many of you, because they’re very old school. For instance, Strevens is very much in favor of the traditional system of peer-reviewed scientific papers and all their conventions (dry language, strictures against speculation, etc.). He thinks it’s best if most scientists don’t pay attention to philosophy or other “ways of knowing”. He does not think that most scientific work involves, or should involve, much in the way of creativity. He thinks it’s good that science rewards scientists who are willing to spend inordinate time and effort on tedious data collection. Etc.
• I found myself wondering if there are analogues of the iron rule in other fields. For instance, think of the old saying in software engineering, “code wins arguments“.

My criticisms and questions:

• Strevens sometimes resorts to hypothetical examples rather than actual historical examples to illustrate his ideas. This is a letdown because the historical examples are so well-told, and because some of the hypothetical examples are a bit weird. I couldn’t see any reason why he couldn’t have stuck to historical examples throughout.
• I think Strevens overgeneralizes from physics, and particularly from his hero Newton. In particular, I disagree with his chapter suggesting that “beauty” might constitute a partial exception to the iron rule. I know lots of physicists these days say that the “beauty” of a theoretical claim is a reliable guide to its truth. But I think Sabine Hossenfelder demolished that idea within physics. And it’s notable that scientists who aren’t physicists hardly ever stump for “beauty” as a reliable, data-independent marker of truth.
• Strevens’ emphasis on implementing the iron rule via testing the quantitative predictions of phenomenological models also represents an overgeneralization from physics, I think. Yes, you can test Newton’s laws of motion, and quantum mechanics, without understanding why those laws work. But I feel like attempts to develop and test purely phenomenological models have a pretty mixed track record in science as a whole. Strevens is right that testing the predictions of purely phenomenological models is a way to implement the iron rule. But he kind of leaves the impression that it’s the only way, which it isn’t. I left the book fairly convinced that the iron rule is right, but less convinced by Strevens’ elaborations on how to apply the iron rule in practice.
• I wish I knew more about Isaac Newton, to be in a better position to evaluate Strevens’ comments on Newton. Strevens’ presents Newton as more or less the inventor of modern science, because he invented the iron rule. In Strevens’ telling, Newton was a rare genius capable of compartmentalizing his scientific research from his other interests (his alchemical work, his work in Christian history and theology, etc.). So that Newton consciously followed the iron rule in his scientific work, while consciously ignoring the iron rule in his non-scientific work. I’m just instinctively suspicious that Newton himself saw a clear bright line between his scientific work in the Principia and his work in alchemy or whatever.
• Strevens’ answer to his second big question–why science emerged relatively suddenly in 17th century Europe–isn’t very convincing, though I don’t really know enough history to judge. It’s basically just a list of favorable preconditions to adoption of the iron rule that were operative in Europe in the 17th century, plus the claim that Isaac Newton was a genius. There’s no discussion of why science didn’t emerge earlier in other places where some or all of those conditions held. And there’s no discussion of whether science could’ve emerged under some other set of conditions. As an exercise in counterfactual history, it’s too brief and superficial to be very convincing. (Click that last link for a more convincing exercise in counterfactual history of science.) But in fairness, most of the book is about Strevens’ first question–what distinguishes science from non-science. You can definitely read the book as an answer to the first question and not worry about the answer to the second question.

Bottom line: Brian and I have previously recommended some “philosophy of science 101” readings for ecologists, but having read Strevens’ book I think I’d recommend it instead. Strevens’ book is more fun to read and accessible than intro-level philosophy of science textbooks, such as Peter Godfrey-Smith’s Theory and Reality. Though it kind of depends what you want. Do you want the sort of piecemeal, haphazard introduction to philosophy of science that you’d get from reading philosophy of science papers about some bit of ecology? Or do you want a systemic, “big picture” introduction to philosophy of science that doesn’t mention ecology at all?

Here are links to other reviews from Science, the NYTimes, and the Guardian. And here’s a video of Strevens discussing his book.