Tom Chivers puts Bayesโ theorem in plain English and it sounds almost obvious: โthe probability of event A, given event B, equals the probability of B given A, times the probability of A on its own, divided by the probability of B on its own.โ A formula for revising what you believe when new evidence arrives. You started somewhere. Something changed. Now you believe something slightly different. Repeat.
The obvious part is the mechanics. The hard part is the loop.
Most reasoning errors I catch in myself arenโt failures of logic โ theyโre failures to update. I hold a view, evidence accumulates against it, and I find reasons the evidence is flawed rather than reasons the view might be.
Psychologists have a name for this: confirmation bias. But Iโve always found that label a bit too clean, like it describes a bug rather than a feature.
The prior isnโt wrong to be sticky. It represents everything youโve learned up to this point. The problem is when it becomes load-bearing โ when the prior stops being a starting position and starts being a conclusion.
โStrong opinions, loosely heldโ is supposed to solve this. Itโs a useful phrase โ it captures something true about the right posture toward your own beliefs. But in practice the second half is harder to honor than it sounds. The strong opinion gets stated, new evidence arrives, and changing your mind in public feels like losing. The โloosely heldโ part quietly becomes decorative.
What Bayes actually demands is something closer to epistemic humility with arithmetic attached. You donโt get to say I donโt know. You have to say I estimate 0.4, and here is what would move me to 0.6. Thatโs harder. It requires you to specify not just what you believe but how youโd know if you were wrong.
This is why Bayesian thinking keeps surfacing in AI conversations. Modern language models do something structurally adjacent to this โ not consciously, but mechanically. Every token generated is a probability distribution revised forward by context. The model doesnโt know the next word; it updates a prior over all possible words, given everything that came before. Itโs not reasoning the way humans reason, but itโs updating the way Bayes updates: continuously, contextually, without the luxury of certainty.
Whether thatโs comforting or unsettling probably depends on your own prior.
The deeper thing Chivers is pointing at, I think, is that Bayesian reasoning is essentially a description of intellectual honesty as a process rather than a trait. You canโt just decide to be open-minded. You have to build the loop: form a belief, assign it a probability, watch for evidence that should move it, and then actually move it. Most of us do the first three. The fourth step is where it gets expensive.
Iโve been wrong about enough things by now that Iโve started to treat my own confident views with mild suspicion. Not paralysis โ you have to act on something โ but a background awareness that the prior Iโm acting on was formed by a person who had less information than I do now, and less than Iโll have next year.
Strong opinions, loosely held, sounds right. The trick is meaning it.


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