Chapter 2 of 66 min
Surfacing assumptions
Every argument rests on assumptions, and most errors hide there. Making assumptions explicit lets you test them before they cost you.
Key ideas
- Unstated assumptions are the weakest links in reasoning.
- The most dangerous assumption is the one everyone shares.
- Testing one key assumption is worth more than polishing the analysis.
Step by step
- 1
Write your conclusion in one sentence.
- 2
List what must be true for it to hold.
- 3
Rate each assumption by confidence and impact.
- 4
Test the highest-impact, lowest-confidence assumption first.
Example
A team plans a product launch assuming customers will pay monthly. A ten-customer test shows they prefer annual billing, and the pricing changes before launch.
Your drill
Take a decision you are about to make. List five assumptions and find a quick way to test the riskiest.
Common mistakes
- Listing only comfortable assumptions.
- Treating confidence as evidence.
Check yourself
Which assumption should you test first?
Show the answer
The one with the highest impact on the conclusion and the lowest confidence.
Saved in this browser. Create an account to keep your progress on every device.
Practise this chapter with your AI coach
Create a free account to practise this chapter in Reasoning Lab, get specific feedback on every answer and keep your progress.
Start free