The world is complex, Richard Posner observes in his most recent book, Reflections on Judging. It follows that, for judges to achieve “sensible” resolutions of real-world disputes—by which Judge Posner means “in a way that can be explained in ordinary language and justified as consistent with the expectations of normal people” (p. 354)—they must be able to navigate the world’s complexity successfully. To apply legal rules correctly and (where judicial lawmaking is called for) to formulate legal rules prudently, judges must understand the causal mechanisms and processes that undergird complex systems, and they must be able to draw sound factual inferences from multivocal or opaque data. The problem that animates the book is that, thanks to s...