Duplicate this page before you start, and write your answers in your own copy.
The Müller-Lyer illusion (Wikimedia Commons)
https://www.youtube.com/watch?v=2RSsoTJA6cA
✍️ Before you read on, write here: look at the image. Which line is longer?
The two lines are exactly the same length. Measure them if you do not believe it.
✍️ Write here: now that you know, look again. Can you stop seeing the difference? What does that tell you about how you came to "know" which line was longer?
Each of these people knows something. Read them all before you write anything.
A. Words for snow
The often-cited claim that Inuit peoples have dozens of words for "snow" is used to show how vocabulary shapes how we categorise and understand the world. Whether or not this specific claim is accurate, the principle holds: people who need to distinguish between types of snow (for survival) develop words that allow them to think about and discuss distinctions that others might not even notice.
B. The discovery of Neptune
In 1846, astronomers noticed that Uranus wasn't orbiting exactly as Newton's laws predicted. Using logical thinking and mathematical calculation, they inferred that another planet's gravity must be affecting Uranus. They calculated where this unknown planet should be, pointed their telescopes there, and found Neptune: a planet found through mathematics and logic before anyone had seen it.
C. A witness in court
A witness to a crime recalls seeing a blue car speeding away. Six months later in court, they testify confidently about what they saw. But research shows that human recall is reconstructive: we unconsciously fill in gaps and can be influenced by suggestion. If a police officer asked, "Did you see the blue car?" rather than "What colour was the car?", this might have planted or reinforced what the witness now remembers.
D. The wine taster
Professional sommeliers can identify a wine's grape variety, region, and even vintage year just by tasting and smelling. Their highly trained senses allow them to detect subtle differences that most people miss, such as hints of oak, levels of tannins, and fruit notes.
E. The chess grandmaster
A chess grandmaster glances at a complex board position and immediately "knows" the best move, often without being able to fully explain why. Years of experience have trained them to recognise patterns instantly. Novice players need to think through each possibility step by step.
F. Trusting the science
When you read that climate change is caused by human activity, you may accept this on the basis of scientific consensus. But you personally haven't reviewed all the data, run the experiments, or checked the mathematics. You trust the scientific process, peer review, and the expertise of climate scientists.
G. Reading Anne Frank's diary
When historians and students read Anne Frank's diary, their feelings (empathy, sadness, horror) help them understand the human reality of the Holocaust in ways that statistics alone cannot convey. These feelings don't replace factual knowledge; they deepen understanding of what those facts meant for real people.
H. Einstein's thought experiments
Einstein imagined riding on a beam of light and asked himself what he would see. He pictured standing in a lift in space and wondered whether he could tell the difference between gravity and acceleration. These mental scenarios, not laboratory experiments, helped lead him to the theory of relativity.
✍️ Write here, on your own: for each knower, what were they relying on to know? Use your own words. Some may be relying on more than one thing.
| Knower | What they relied on |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F | |
| G | |
| H |
Choose two of the four scenarios below and answer their questions.