Thinking tools
First principles
Break a problem down to what you know is true and reason up from there, instead of copying what others have done.
Aristotle, who held that every demonstration must start from first principles (archai) that are known without being proved.
Reasoning by analogy says: things like this usually cost this much, work this way, take this long. Reasoning from first principles asks what the thing is made of, what physics or arithmetic says about it, and what follows from those facts alone. Aristotle described knowledge as a chain of deductions that has to stop somewhere, at starting points that need no further proof.
Analogy is fast and usually right, which is why it is the default. Its weakness is that it carries over every assumption baked into the thing you are copying, including the ones that stopped being true years ago. Going back to base facts exposes those inherited costs and constraints, and that is where large improvements tend to hide.
It is slow and expensive, so use it on the few problems where the conventional answer looks badly wrong. People also misuse the label. Calling an untested opinion a first principle does not make it one; the base facts have to be things you can measure or check.
Example
Before founding SpaceX in 2002, Elon Musk found that buying a rocket was very expensive. He asked what a rocket is made of (aerospace aluminium alloys, titanium, copper, carbon fibre) and what those materials cost on the commodity market. In a 2012 interview with Wired he said the materials came to around two percent of the typical price, which became the case for building rockets in-house.
Where it applies
When a vendor quote, a cloud bill or a model's inference cost looks fixed, compute what the underlying compute, storage and bandwidth actually cost. In system design, ask what the hard limits are (latency of light, memory bandwidth, token budget) before accepting how the last team did it.
Think about it
Which cost or constraint in your work do you accept only because everyone else accepts it?
Applied it to something real? Log it.
Test yourselfWhat is the difference between reasoning by analogy and reasoning from first principles?
Analogy copies what similar things do, along with their assumptions. First principles starts from facts you can verify and builds the answer up from them.
Related models
- Occam's razorWhen several explanations fit the evidence equally well, prefer the one that needs the fewest extra assumptions.
- The map is not the territoryEvery model, metric or plan is a simplification, and the parts it leaves out can matter more than the parts it shows.
- Chesterton's fenceBefore you remove a rule, a process or a piece of code, find out why someone put it there.
- Thought experimentsRun an experiment in your head, following an idea to its consequences, when the real experiment is impossible, expensive or not yet needed.
- AnchoringAny number you see before estimating pulls your estimate towards it, even when you know the number is random.