---
title: "Telling a Cause From a Coincidence"
description: "Two things moving together is not one causing the other. Test a causal claim about the past by checking the order of events, hunting for a third factor that could explain both, and asking what evidenc"
canonical: https://lightmysky.com/learn/history/telling-a-cause-from-a-coincidence-mt_SN1oFNj2gb
source: https://lightmysky.com/learn/history/telling-a-cause-from-a-coincidence-mt_SN1oFNj2gb.md
retrieved: 2026-09-12
---

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# Telling a Cause From a Coincidence

Two things moving together is not one causing the other. Test a causal claim about the past by checking the order of events, hunting for a third factor that could explain both, and asking what evidence would count against the claim.

Subject: History · Area: Historical Thinking · Ages 15 to 16
Page: https://lightmysky.com/learn/history/telling-a-cause-from-a-coincidence-mt_SN1oFNj2gb

## Ready when they can

- Give a case where two historical trends moved together without either causing the other
- Check that a proposed cause actually came before the effect it is offered for
- Name a third factor that could explain both of two linked changes
- Say what evidence would count against a causal claim you have just made

## Lesson: Together is not because

Two things moving together is not one causing the other. Correlation means they rise and fall as a pair, while cause means one brings the other about through a path you can name. When you read that one event caused another, your first job is to refuse the shortcut.

Run two checks before you believe any causal claim. First the order check: the proposed cause must come before the effect, so if banks spread after mills were built, banks did not start the mills. Then the mechanism check: coal could power steam that ran machines, and that chain holds because each link touches the next.

**Example.** Plague deaths and wage rises moved together in the 1300s, but germs did not sign pay deals. Fewer workers meant lords competed for hands, and that bargaining lifted pay. Labour shortage is the third factor here: one change explaining both halves at once. Ice cream sales and drownings work the same way, with summer heat driving both.

**Tip.** Always ask what evidence would count against your own claim. A find showing the effect came first, or a link in your chain failing its test, should sink it. If no possible find could shake you, you are preaching, not reasoning, and good historians hunt the proof that could prove them wrong.

**Recap.** Check order, name the path, hunt the third factor, and state what would prove you wrong.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Weighing a Source's Reliability](https://lightmysky.com/learn/history/weighing-a-sources-reliability-mt_24TQ9c30NI)
- [Weighing Historical Causes](https://lightmysky.com/learn/history/weighing-historical-causes-mt_BjY92Ahl-S)

## Opens up

- [Contingency: What Almost Happened](https://lightmysky.com/learn/history/contingency-what-almost-happened-mt_bTs2PTs8a-)
- [Why Historians Disagree](https://lightmysky.com/learn/history/why-historians-disagree-mt_qSzuXmTEJz)