Causation vs Correlation: Understanding Why Things Happened

One of the most dangerous sentences in history is: “The numbers speak for themselves.” A city bans alcohol and deaths fall. A factory upgrades machines and profits rise. A new policy starts and crime drops. But here’s the twist: all three stories can be true—and still not be causal.

Here’s where thinking like a historian gets interesting: you almost never get to run the perfect experiment. You can’t rewind the 1854 cholera outbreak and try it again without removing the pump handle. You can’t re‑run Prohibition in a parallel United States where the law never passed. Yet historians still make strong claims about why things happened: why revolutions ignite when they do, why empires collapse, why social movements suddenly gain traction after years of failure.

To do this, they lean on patterns across time and space: comparing similar cities with different laws, tracing sequences of events, and hunting for plausible mechanisms in letters, speeches, and statistics. You’ll notice they ask not just “what changed?” but “what else changed at the same time—and who benefits from which story of cause and effect?”