First Principles: Reasoning From the Ground Up

There are two ways to attack a problem that everyone calls impossible, or merely expensive. The first is reasoning by analogy: look at how the thing has always been done, what it cost last time, what the market charges, and shave a little off. Analogy is fast, sociable, and usually right — which is exactly why it fails at the moment the inherited answer is itself the problem. The second way is slower and ruder: refuse the inherited answer, take the problem apart until the pieces are facts, and rebuild the answer from there. That is first-principles reasoning, and it is less a talent than a refusal — the refusal to let how things are done stand in for how they work.

An old name for the floor

The term belongs to philosophy long before it belonged to any founder. Aristotle called the starting points of a science archai — first principles: in the Posterior Analytics, the propositions a field cannot demonstrate because they are what its demonstrations stand on, the floor where proof stops and reasoning starts. Physics kept the habit alive longest. Before asking what a thing costs, or how it is conventionally built, ask what it is made of and what the laws of nature permit. A first principle is not an opinion held strongly. It is what would still be true if every convention surrounding the problem disappeared overnight.

The battery, in his own telling

The modern popularizer is Elon Musk, who has described the method in interviews for well over a decade — at TED in 2013, as boiling things down to the most fundamental truths and reasoning up from there, as opposed to reasoning by analogy. His standard illustration is the battery pack. The industry, in his telling, “knew” that battery packs cost about $600 per kilowatt-hour and would not get much better. He asked a different question: what is a battery actually made of? Cobalt, nickel, aluminum, carbon, some polymers for separation, and a steel can. And what would those materials cost, bought on the London Metal Exchange? His figure was roughly $80 per kilowatt-hour — which would mean most of the famous $600 was not physics at all, but the way the industry had organized itself, and could be organized differently. He tells the same story about rockets, whose raw materials he has put at roughly two percent of a finished rocket’s price. Read the numbers as what they are: one founder’s illustrations from his own interviews, not audited accounts. The transferable asset is the question — and Musk himself is candid about its price, noting that thinking this way takes a great deal of effort and cannot be how you think about everything. It is a tool reserved for the problems where analogy has stopped working.

The same instinct, wearing a suit

You do not need a rocket company to make the move; the consulting world industrialized a cousin of it. As described in published accounts of McKinsey & Company’s working method — Ethan Rasiel’s The McKinsey Way, written by a former consultant there, is the accessible one — the discipline runs: state an initial hypothesis, then decompose the problem into an issue tree whose branches are MECE — mutually exclusive, collectively exhaustive, no overlaps and no gaps — and test the hypothesis branch by branch. An issue tree is first principles with the poetry removed. The problem is not accepted in the shape it arrived in; it is taken apart until every piece can be examined on its own evidence, with nothing double-counted and nothing quietly dropped along the way.

Run it, then, in four moves. Name the assumption dressed as a fact — “batteries cost $600” in the famous case; “that’s just what this process takes” in most offices. Take the problem apart until the pieces are physical facts, contract terms, or human behaviors rather than conventions. Rebuild the answer one level at a time, and mark every place where the rebuild disagrees with the standard answer — the disagreement is where the value is hiding. And stop when the pieces stop changing the decision. Analogy remains the right tool for most of the week. First principles is for the handful of problems where being conventionally right is the most expensive option on the table.

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