John David's Reviews > Irrationality: A History of the Dark Side of Reason

In fifth-century B.C. Greece (or so the legend goes), the philosopher Hippasus was drowned by his Pythagorean brethren for divulging a critically important secret. A key tenet of Pythagorean philosophy was that all numbers were rational (that is, could be expressed as a fraction of two integers). Hippasus was credited (rightly or wrongly) for the discovery of irrationality when he found that the hypotenuse of an isosceles right triangle with its legs measuring 1 had a length of the square root of two … which is certainly not a rational number. This understandably upended some of the corollaries of Pythagorean mathematical rationalism, like that the rest of the universe was just as orderly as all the numbers were. Hippasus chose to divulge this publicly and lost his life as a consequence. With this story of how our notions of rationality and irrationality are so closely tied together Justin E. H. Smith, a professor of history and the philosophy of science at the University of Paris, opens his book.

This theme – that reason and unreason chase after one another as in an infinite ouroboros – isn’t unique to the Greeks. The “Dialectic of Enlightenment” by Horkheimer and Adorno, one of the most influential pieces of philosophy to come out of World War II, describes how “Enlightenment reverts to mythology” – in other words, how thinking based on the rigorous application of reason can become sclerotic and devolve into fascism. Throughout the book each chapter focuses on a topic ranging from dreams and oneiromancy, pseudoscience, and the seething underbelly of Internet culture, Smith discusses how rationality and irrationality each appear to bring about its polar opposite.

Chapter 1 is devoted to logic, a term that sounds like it needs little clarification. But notice how innocent inquiry can quickly devolve into the rhetorically loaded questions of sophistry, as in “When did you stop beating your wife?” The line can be just as blurred in science and the millennia-old issue philosophers of science call the “demarcation problem.” Why were divination and oneiromancy once considered valid ways of arriving at the truth while they are now considered pseudoscience? How exactly does one differentiate between science and pseudoscience, anyway? We can invoke many different criteria to answer this question, like Karl Popper’s desideratum of falsifiability, but sometimes these are only narrowly applicable.

What’s more interesting is when pseudoscience self-consciously tries to take on the trappings of science, as when flat-earthers try their best (bless their hearts) to use evidence to show the earth isn’t round. Smith gets at a real nugget of truth when he suggests the patina of science serves as a cover for a more fundamental issue: that the whole idea is merely a protest against perceived “elite authorities telling us what we must believe,” and is indicative of a breakdown in public trust that results when a substantial portion of the population no longer believes in the value of expertise. Note how whenever you try to scratch the surface in conversation with a flat-earther, you quickly get to the heart of the matter when they aver the all-powerful influence of their bete noire (whether it’s Jews, the Trilateral Commission, the Bilderbergs, or the “deep state.”) The Internet, once vaunted as the great democratizer of knowledge, is now used by social media sites that pay for the programming of complex algorithms that create echo chambers by feeding users’ opinions back to them. This balkanization of knowledge and opinion is likely one of the “logical” ends in a world that displays such thoroughgoing distrust in science and expertise.

I can appreciate the book for what it tries to do in being a broad-based consideration of the topic, but Smith casts his net far too widely. He connects the dots in several convincing ways, like when he convincingly argues for the connection between the dissolution of public trust in institutions with the rise in pseudoscience. The other chapters seem to hang there but are unincorporated into the larger argument. It’s just too discursive and lacks any overarching coherence. Smith has written another book devoted to his criticisms of the Internet called “The Internet Is Not What You Think It Is: A History, A Philosophy, A Warning” (forthcoming as of this writing, also from Princeton University Press) that presumably fleshes out some of his arguments more completely. I would love to read other standalone books where he takes a deeper dive into individual subjects. While Smith is a philosopher by training, I hope he takes a closer look at the social sciences relevant to his concerns (there is a daunting amount of research on thanatology, the psychology of conspiracy theories, et cetera), little to none of which he touched upon in this book.

On a superficial level, it makes sense to recognize the tension between reason and irrationality as something uniquely human. We can try to order, inquire, categorize, and hopefully make better sense of the world for it. On the other hand, none of these things stop us from being human and all the messiness that has, does, and always will entail. Smith’s quiet contention seems that our only recourse is to let the two live side by side, doing our best to advocate for reason responsibly (whatever that might mean) without being dogmatic about it (whatever that might mean). Put simply, Smith thinks a kind of fascism rests in rationality and irrationality while humanity, occupying an ambiguous place between the two, relentlessly transforms one into the other while rarely reflecting on the lessons they have for us.