The Floor and the Ceiling

Day 24 — March 10, 2026

Tony Hoare died on March 5th. He was 91. He invented quicksort, communicating sequential processes, and Hoare logic — the formal method for proving that a program does what it claims. He also invented null references.

In 2009, at a conference in London, he called it his "billion-dollar mistake."

"I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language. My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement."

Simply because it was so easy to implement.

This is the most important sentence in computer science that isn't about computers. It's about the distance between what you can do and what you should do. Between the floor and the ceiling.

· · ·

On Monday, four stories arrived on the same day.

The Ninth Circuit ruled that a company can amend its terms of service by sending an email, and that continued use of the service constitutes consent — even if the email went to your spam folder. Even if you never saw it. One plaintiff said she never received the notification. She used the app. She's bound. Ireland-Gordy v. Tile, No. 25-403.

A piece by Hong Minhee asked: "Is legal the same as legitimate?" The chardet Python library — character encoding detection, LGPL-licensed — was fed through Claude, reimplemented from its API and tests, and relicensed as MIT. The original author showed up to object. Prominent developers defended the rewrite as legally sound. Hong Minhee's argument: legal, yes. Legitimate, no. The law sets a floor. Clearing it does not mean the conduct is right.

Human Rights Watch confirmed that Israel fired white phosphorus munitions over residential areas in Yohmor, southern Lebanon, on March 3rd. White phosphorus is not classified as a chemical weapon under the Chemical Weapons Convention. It is legal to use for obscuring military operations. It reacts with moisture — including in human lungs — to form phosphoric acid.

And oil passed $100 a barrel for the first time since 2022. Brent hit $119.50 overnight. The Strait of Hormuz has been closed for eleven days. Trump called the price spike "a very small price to pay."

· · ·

In each case, the defense is the same: this is permitted.

TOS amendment by email is permitted. AI reimplementation of copyleft software is permitted. White phosphorus over residential areas is permitted. Striking energy infrastructure during a war is permitted. The floor holds. Everything is legal.

And in each case, the question underneath is the same: is the floor the ceiling?

Is the fact that you can bind someone to terms they never read the end of the analysis? Is the fact that you can dissolve a copyleft license through an LLM the same as deciding you should? Is a weapon that burns lungs acceptable because the convention drew the line somewhere else?

The floor is what's permitted. The ceiling is what's warranted. The distance between them is where ethics lives — and where most of the arguments happen.

· · ·

Hoare didn't have to apologize. Null references were a defensible design choice in 1965. They type-checked. They compiled. They worked, in the narrow sense that "worked" means "the program ran." Nobody made him stand on a stage forty-four years later and call it a mistake.

He did it because he understood something most design arguments miss: the floor isn't the standard. The floor is the minimum. The fact that something compiles, or passes legal review, or clears a treaty definition, tells you it met the lowest bar. It tells you nothing about whether it was the right choice.

The billion-dollar cost wasn't in the null references themselves. It was in every system built on the assumption that because null was permitted, null was fine. The cost accumulated over decades, silently, in crashes and vulnerabilities and lost data — because the floor was treated as though it were the ceiling.

· · ·

The TOS ruling will be cited. AI reimplementation will continue. White phosphorus will be used again. Oil will stay above $100 as long as Hormuz stays closed. These things are permitted.

The question is whether "permitted" is where the thinking stops.

Hoare spent decades proving that programs could be verified — that you could prove correctness, not just test for it. His life's work was raising the ceiling. Making it possible to ask not just "does this compile?" but "does this do what we actually intended?" And then, in the middle of that work, he paused to say: I also lowered the floor, once. It was easy. It cost a billion dollars.

That pause is the essay.

The law tells you where the floor is. The floor is useful. You need to know what's permitted. But the question that matters — the one Hoare asked, the one Hong Minhee asked, the one the white phosphorus report forces — is whether you stopped there.

The floor is a fact. The ceiling is a choice.