🧠Critical Thinking·15 min·Sample Lesson

Spot the Assumption: Thinking Like a Detective

Imagine you walk into your kitchen and see a broken cookie jar on the floor and cookie crumbs on your dog's nose. It's tempting to shout, 'The dog broke the jar!' But wait — did you actually see it happen? Or did you just assume it, because the evidence seemed to point that way? Good detectives, scientists, and thinkers all share one skill: they notice their own assumptions before deciding something is true.

What You'll Learn

- What an assumption is, and how it's different from a fact - Why jumping to conclusions can lead you to the wrong answer - A 3-step method for checking your own thinking - How real detectives and scientists test assumptions before trusting them

Fact vs. Assumption

A fact is something you can check and confirm is true — 'the cookie jar is broken' is a fact, because you can see it. An assumption is something you believe is probably true, but haven't actually confirmed — 'the dog broke it' is an assumption, because maybe your little brother did it and blamed the dog, or the jar was already cracked and just fell on its own. The danger isn't having assumptions — everyone does — it's forgetting that they're assumptions and treating them like proven facts.

The 3-Step Assumption Check

Step 1: Ask 'What do I actually know for certain?' List only the facts you directly observed. Step 2: Ask 'What am I filling in with a guess?' This is your assumption. Step 3: Ask 'What's one other explanation that fits the same facts?' If you can think of even one other explanation, you know you were assuming, not proving. In the cookie jar example: Fact = jar is broken, crumbs on dog's nose. Assumption = dog broke the jar. Other explanation = a person broke it and then let the dog eat the fallen cookies afterward.

How Real Detectives Do This

Detectives are trained specifically not to assume the first suspect is guilty. In real investigations, police look for an alibi — proof someone was somewhere else — precisely because an assumption based on 'it looks bad for them' has led to wrongly accusing innocent people in real history. That's why courts require evidence, not just a story that sounds believable.

Scientists Do This Too

When scientists see a pattern, like ice cream sales and shark attacks both going up in summer, a careless thinker might assume ice cream causes shark attacks. A careful thinker asks what else could explain both: warmer weather means more people buy ice cream AND more people swim in the ocean. The real cause was hiding behind an assumption.

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What is the key difference between a fact and an assumption?

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In the cookie jar example, what was the assumption?

Match each statement to whether it is a FACT or an ASSUMPTION in the cookie jar story.

Terms

The cookie jar is broken

There are crumbs on the dog's nose

The dog broke the jar

No one else could have done it

Definitions

FACT - directly observed

ASSUMPTION - not directly seen

Drag terms onto their definitions, or click a term then click a definition to match.

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Assumption Detective Notebook

Think of a real mini-mystery from your own life this week (a missing snack, a messy room, a broken toy). Using the 3-Step Assumption Check, write: (1) the facts you actually observed, (2) the assumption you almost made, and (3) at least one other explanation that fits the same facts. Deliverable: a half-page 'detective notebook' entry with all three parts clearly labeled.

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