First Principles Thinking

Break a problem down to its basic truths (axioms) and build up from there, rather than reasoning by analogy ("doing what others do").

What's your IQ?

Take the IQ test

25 questions · about 12 minutes

What would you score? Try question 1.

Which option completes the grid? One tap, no sign-up.

A reasoning model. All mental models

How it works

First Principles Thinking is a cognitive framework that changes how you see problems. Once you understand it, you'll notice opportunities to apply it everywhere.

This model works because it strips away irrelevant detail and exposes the core structure of a problem. Most people reason by analogy ("what do others do?"); this framework forces you to think from first principles.

How to apply it

Don't just improve the horse; invent the car. Question every assumption until you hit a law of physics.

Example

Elon Musk used this to build cheaper rockets by calculating the raw cost of materials rather than buying finished parts.

When to use it

This model is most useful when you're stuck. If your current approach isn't working, First Principles Thinking often reveals the hidden constraint.

Common mistakes

Over-applying: Not every problem benefits from this model. Match the tool to the situation.
Under-applying: People learn the model but don't practice it. Application takes repetition.
Misunderstanding the principle: Surface-level understanding leads to poor execution. Study the examples.
Ignoring context: The same model works differently in different domains. Adapt accordingly.

Practice exercises

Identify a current decision you're facing. Write down the assumptions you're making. Challenge each one.
Look at a past failure. Apply First Principles Thinking retroactively: would it have changed the outcome?
Teach the model to someone else. If you can't explain it simply, you don't understand it well enough.
Set a reminder to apply this model once per week for the next month. Track the results.