(2025-04-11) Alexander Come On Obviously The Purpose Of A System Is Not What It Does

Scott Alexander: Come On, Obviously The Purpose Of A System Is Not What It Does. (POSIWID) Consider the following claims: The purpose of a cancer hospital is to cure two-thirds of cancer patients.

The purpose of the Ukrainian military is to get stuck in a years-long stalemate with Russia.

These are obviously false.

Am I being unfair here? Maybe the slogan “the purpose of a system is what it does” was never meant to apply to situations like these?

It’s only used for galaxy-brained claims like “The purpose of a system is what it does! The police do a bad job solving crime, therefore the purpose of the police must be to tolerate crime, no matter what you gullible starry-eyed idealists who take the police’s story at face value might think!”

Here the correct response is that the police might try to solve crime, but fail

*Or someone might say “The police sometimes brutally beat suspects. Therefore, the purpose of the police is to control and intimidate the population by brutally beating them. You can’t claim that this is just a mistake or a side effect - the purpose of a system is what it does!”

Here the correct response is that you can absolutely claim it is an unfortunate side effect*

These people are just taking the single worst and least-desired side effect of a system, then asserting that this - and not any of the much more reasonable things that the system does - must be its one true purpose.

If you feel tempted to say “the purpose of a system is what it does”, I recommend at least coming up with some novel rephrasing. How about “No system has ever failed at its purpose”? Or “There is no such thing as an unintended consequence”? At least then everyone would know where you stand!

Highlights From The Comments On POSIWID

Many people argued that the phrase had some valuable insight, but disagreed on what it was. The most popular meaning was something like “if a system consistently fails at its stated purpose, but people don’t change it, consider that the stated purpose is less important than some actual, hidden purpose, at which it is succeeding”. I agree you should consider this, but I still object to the original phrase, for several reasons.

I think the people who use the phrase want to imagine that they’re pushing people from Naive to Balanced. But I think the last person to hold the Naive perspective died sometime in the 1980s, and in real life POSIWID is mostly used to push people from the Balanced to the Paranoid perspective without actually looking at the system involved or arguing the case.

Hopefully this will become clearer as I answer your comments one by one, starting with:

When people insist on the confusing and inappropriately-strong version, I start to suspect that the confusingness is a feature, letting them smuggle in connotations that people would otherwise correctly challenge.

Ersatz writes:
“I thought the meaning was more something like “the system took these side effects into account and still considered that what it was doing was net positive in expectation, so the side effects are as much part of the system's purpose as the ‘positive’ outcomes”.
This is just diluting the word “purpose” into incoherence.