Your vase is shattered and your roommate offers two explanations: he bumped the table, or a gang of invisible leprechauns did it. Both fit the evidence, yet you know which to believe. This episode explores Occam’s razor, the law of parsimony, beginning with the irony that William of Ockham neither invented it nor wrote its most famous Latin phrasing, which came from John Punch in 1639, while the name itself appeared in 1649. Aristotle, Ptolemy, Maimonides and Aquinas all used the idea first.

The hosts explain why the justification shifted from medieval aesthetics to Karl Popper’s falsifiability, why ad hoc hypotheses barricade a theory from evidence, and how overfitting in data science captures noise, with a review finding added complexity raised forecast errors by an average of 27 percent. Applications include Newton, Einstein, the zebra rule in medicine and the musk ox debate between group selection and the selfish herd, before Francis Crick’s warning that the razor is dangerous in biology, Walter Chatton’s and Kant’s anti-razors, and Igor Mazin’s inverse Occam’s razor in physics journals.

• Entities must not be multiplied beyond necessity and who actually said it
• Why Ockham suspended his own razor when it came to miracles
• Memorizing past exam questions as an analogy for overfitting
• Morgan’s canon and George C. Williams on individual versus group selection
• A razor, not a bulldozer: using parsimony on a friend who hasn’t texted back