Overlooked Alternative Explanations

Definition

Any given observation is typically compatible with more than one causal story, and rigorous thinking requires actively generating the rival explanations before accepting the one that was handed to you — rather than evaluating a single proposed explanation in isolation and asking only whether it's plausible. The discipline is comparative: not "could this explanation be true?" but "is this explanation more likely than the alternatives, given the same evidence?"

In the Book

Levitin opens with an everyday case — a friend who doesn't return your greeting in a hallway could be angry at you, but could equally not have seen you, been late, or been preoccupied — before moving to higher-stakes cases. When CERN physicists reported neutrinos apparently traveling faster than light, the mundane alternative explanation (a loose cable causing a measurement error) turned out to be correct, illustrating that a methodological flaw is almost always more likely than an explanation requiring you to rewrite physics. He extends this into legal reasoning: in the case of Dennis Adams, convicted on DNA evidence alone, the court never seriously weighed the alternative hypothesis that his brother — whose DNA would also match — committed the crime, because no additional evidence pointed to the brother specifically; Levitin argues courts should be comparing the probability of guilt given the evidence against the probability of innocence given the same evidence, not evaluating the prosecution's story alone. He also applies the concept to failed forecasting, quoting Will and Ariel Durant's 1968 prediction that Catholic birth rates would make Catholicism dominant in U.S. politics by 2000 — a forecast that ignored the alternative scenario (falling religious observance, contraceptive use) that in fact occurred.

Why It Matters

This concept converts single-hypothesis evaluation into comparative hypothesis evaluation, which is the difference between "does this story fit the facts?" (almost any story can be made to fit) and "is this story the best available explanation of the facts?" It applies wherever a compelling narrative is offered for an observation — pseudoscience, forecasting, criminal trials, diagnosis, root-cause analysis in engineering or business — because a single unchallenged explanation, however plausible-sounding, has not actually been tested against its competitors.