Concept 7 of 8
Substitution Chain: Rename, and Rename Back
Today's big idea
Given the real thing take the rule's right side; given the new name take its left.
One rule answers both: what a cup is now called, and what a plate really is.
How it works
👀 What's going on?
Some questions rename everyday words before asking anything at all. At Class 4 they always run forwards, from the real thing to its new name. At Class 5 they run backwards too, handing you the new name and asking what it really is.
💡 Here's the trick
Look at the rules above. Going forwards, you answer honestly first, so tea comes from a cup, and only then look up that a cup is called a plate. Going backwards you do the opposite. To find what is really called a bowl, hunt for the rule with bowl on its right-hand side. That rule is plate is called bowl, so a bowl is really a plate.
🪄 How to do it
- 1.Decide which way the question runs, as the rules above can be read from either side.
- 2.Going forwards, answer honestly, then find the rule whose left side is your answer.
- 3.Going backwards, find the rule whose right side is the name you were given, and take its left side.
✍️ Try it
Rules: water is called milk, milk is called juice, juice is called soda. What do you drink when you are thirsty? And what is really called juice?
You really drink water, and water is called milk, so the answer is milk. For the second, juice sits on the right of milk is called juice, so the thing now named juice is really milk as well. The same word, reached down two different roads.
⚠️ Watch out
You might be thinking a backward question can be answered by reading the same rule forwards. It cannot. Reading water is called milk forwards tells you what water is now called, not what the word milk now hides.
🌟 Why this matters
Following instructions in the order the job needs, rather than the order they are written in, is the whole skill. Codes, nicknames and translations all run both ways.
Exam tip: Circle the word the question hands you. Which side of the rules it sits on tells you which way to travel.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“sky is called cloud, cloud is called rain, rain is called sky. What is really called a cloud?”
- 1
Which way does it run?
You were handed the new name, not the real thing, so this one runs backwards. 🔁
- 2
Hunt the RIGHT-hand sides
Only one rule ends in cloud: sky is called cloud.
- 3
Take that rule's left side
Whatever now goes by cloud is really the sky. The other two rules are there to distract.
- 4
Answer ✓
the sky
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Decide which way the question travels BEFORE you answer it.
TWO-WAY SWAPPER · ROUND 1 OF 3
Step 1 · which way does this run?
Quick check
✅ VERIFICATION
If ink is called pen, pen is called nib, and nib is called cap, what is really called a nib?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Dictionary Order
Find the deciding letter, then count straight to the position.