Unit 5 of 12 · Your choices · about 3 weeks

First-Principles Thinking: What do we actually know for sure?

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Most reasoning is reasoning by analogy: we do something because that is how it is usually done. That is efficient and usually fine. First-principles thinking asks a different question — what are the basic facts here, and what could be built from them — and it is how genuinely new solutions get found.

It sits right after decision-making because it is the tool for when none of the obvious options are good enough.

Why does it cost that much?

  1. Pick a simple object the child wants — a skateboard, a pizza, a birdhouse.
  2. List its raw parts and materials. Look up or estimate what each costs on its own.
  3. Compare the sum to the store price. Where did the rest of the money go? (Labor, tools, shipping, the store, profit, design.)
  4. Ask: which of those could we do ourselves, and which are worth paying for?

Core ideas

  • Reasoning by analogy copies existing solutions; first principles starts from basic facts.
  • Ask "why?" repeatedly until you reach something that is simply true.
  • Separate assumptions ("it has always been done this way") from constraints ("water boils at 100°C at sea level").
  • First principles is slower — use it when the usual answer is not good enough.

Activities

The Five Whys

Take a household rule or habit and ask why five times in a row. Find which answers are real constraints and which are just habits.

Pizza from scratch

Cost out a homemade pizza ingredient by ingredient, make it, and compare cost, time and taste to a delivered one.

Redesign challenge

Choose an everyday object that annoys you. Strip it to its purpose, list the true constraints, and sketch a new design that meets them.

One lesson, three outputs

Grades K–2 (ages 5–8)

Take apart a broken toy or appliance (with supervision) and sort the pieces: what does each one do?

Grades 3–5 (ages 8–11)

Do the cost breakdown and the Five Whys, and present one redesign with a labeled drawing.

Grades 6–8 (ages 11–14)

Write a first-principles analysis of a real problem (household energy use, a school-day schedule, a local issue): assumptions, constraints, a proposed solution and its trade-offs.

The family question

Is that a rule of nature, or just how it's usually done?

Thinking Journal prompt

What did I assume was true this week that turned out to be just a habit?

Free resources