Goodhart's Law Is a Prediction, Not a Warning

There is a particular comfort in citing Goodhart's Law. Someone proposes a metric. Someone else recites the line about measures and targets. Everybody nods at the wisdom of it. Then the metric ships on Monday with a bonus attached, and the person who quoted the law feels absolved, because they said the thing. The mistake is grammatical. We hear the law as a warning, which is a mood, not a claim. Read it instead as an indicative sentence about the future. Not "careful, this might spoil". Rather "this will spoil, and here is roughly the date". A short and slightly pedantic historyCharles Goodhart, writing in 1975, was making a narrow point about monetary aggregates. Once a central bank targets a statistical regularity, the regularity dissolves, because the people generating the statistic notice and adapt. Marilyn Strathern gave us the quotable compression in 1997, while dissecting audit culture in British universities, and hers is the version on the mug. Donald Campbell arrived…