# First Principles

> Break a problem down to what you know is true and rebuild from there.

Chapter III, Problem solving · 3.08 · Origin: Aristotle; popularised in engineering by Elon Musk · Time: 20 to 40 min · Solo or group

**Use it when** everyone repeats how it has always been done.

Interactive workspace: https://kogu.tools/tools/first-principles

## Abstract

Most of the time we reason by analogy: we do things the way they've been done before, with small changes. That's efficient, but it carries old assumptions along. First principles thinking separates what has to be true from what's just customary.

You list the assumptions behind the current approach and question each one until you reach things you're sure of, like a physical limit or the price of raw materials. Then you build a solution from those alone. Elon Musk's often-told example is battery packs: he priced the materials inside them and found they cost a fraction of what finished packs sold for.

## Method

1. **Describe the problem and the usual approach.** Write down what you want and how it's normally done.
2. **List the assumptions.** Write down what the usual approach takes for granted about costs, limits and methods.
3. **Question each one.** Ask how you know it's true and what would happen if it weren't. Sort each into fundamental, convention or unknown.
4. **Keep the fundamentals.** Collect the statements that held up. These are your building blocks.
5. **Rebuild.** Design new approaches from the fundamentals alone, treating the conventions as optional.

## When to use it

- Everyone treats a cost or a limit as fixed and you suspect it isn't.
- Small improvements to the current approach have stopped paying off.
- You're new to a field and don't want to pick up all of its habits.

## Common pitfalls

- Questioning everything at once. Start with the assumptions that most affect the outcome.
- Mistaking a strong opinion for a fundamental truth.
- Throwing out a convention without finding out why it exists. Some are there for good reasons.

## References

- Aristotle. Physics, Book I. (c. 350 BCE).
- Aristotle. Posterior Analytics. (c. 350 BCE).