You wore your lucky socks, and your team won. You tried a new coffee shop, and then had a terrible day. The human mind loves these stories—event A happened, then event B followed, so surely A caused B.

This pattern of thinking feels deeply intuitive, yet it leads us astray constantly. The formal name is post hoc ergo propter hoc—Latin for "after this, therefore because of this." Understanding why this reasoning fails, and learning to spot it, is one of the most practical logical skills you can develop.

The post hoc fallacy exploits a genuine truth: causes do precede their effects. If you drop a glass and it shatters, the dropping came first. Our brains evolved to notice sequences and infer causation quickly—a useful survival trait when rustling bushes might mean predators.

But here's the problem. Countless events precede any given outcome. Before your headache went away, you took aspirin, drank water, sat down, checked your phone, and breathed approximately forty times. The aspirin might have helped. So might the water or the rest. Sequence alone cannot distinguish the actual cause from mere coincidence.

Consider how often we fall for this. "I started taking this supplement and felt more energetic." "The economy improved after the new policy." "My cold cleared up once I tried that remedy." Each statement assumes causation from mere timing. The supplement might work, or you might have slept better that week. The policy might have helped, or the economy might have been recovering anyway. Your cold might have responded to the remedy, or it simply ran its natural course.

Takeaway

Sequence is necessary for causation but nowhere near sufficient. When you catch yourself thinking 'A happened, then B happened, so A caused B,' pause—you've only established timing, not connection.

Once you recognize the post hoc pattern, the next step is actively generating alternative explanations. This isn't about being cynical—it's about being thorough. For any sequence, multiple possibilities exist, and good reasoning considers them all.

Start with coincidence—pure chance alignment. Then consider common cause: perhaps a third factor caused both events. You felt better after vacation and started exercising—but maybe reduced stress caused both the good feeling and the motivation to exercise. Next, examine reverse causation: sometimes the relationship runs backward. People who drink moderately might seem healthier than abstainers, but perhaps healthier people feel comfortable drinking while those with health problems avoid alcohol.

Finally, consider natural progression. Many things improve or worsen on their own schedule. Colds last about a week regardless of treatment. Economic cycles rise and fall. If you intervene at a low point, any subsequent improvement might have nothing to do with your action. This is why alternative medicine often "works"—people seek treatment when symptoms peak, then improve naturally and credit whatever they tried.

Takeaway

For every apparent cause-and-effect sequence, practice asking: Could this be coincidence? Could something else cause both? Could the causation run the other direction? Would this have happened anyway?

If sequence alone can't prove causation, what can? The answer lies in systematic comparison. The gold standard is the controlled experiment: take two identical groups, change one thing for one group only, and observe the difference. Any effect can then be attributed to that single change.

In everyday reasoning, we can approximate this logic. Look for variation—does the effect disappear when the supposed cause is absent? Do your lucky socks actually correlate with wins across many games, or just a few memorable ones? Seek consistency—does the pattern hold across different times, places, and circumstances? And examine dose response—if A causes B, does more A typically produce more B?

You can also apply mechanism thinking. Can you identify a plausible pathway from cause to effect? Understanding how something might work strengthens causal claims. Aspirin reduces headaches through specific biochemical pathways we can trace. Lucky socks have no plausible mechanism for influencing distant sporting events. This doesn't prove lucky socks don't work—but it does tell you where to set your initial skepticism.

Takeaway

True causation requires more than sequence—it requires comparison, consistency, and ideally a plausible mechanism. Before accepting any causal claim, ask: What's the comparison group? What happens without the supposed cause?

Post hoc reasoning is everywhere because it feels so natural. Our pattern-seeking minds constantly weave narratives from sequences, and those narratives stick. But feelings of certainty aren't evidence.

The antidote isn't paranoid skepticism—it's disciplined curiosity. When you notice yourself drawing causal conclusions from timing alone, pause to generate alternatives and ask what evidence would actually distinguish cause from coincidence. This habit won't make you cynical; it will make you accurate.