“Pragmatic FDT, and predictors as game theory” by Stuart_Armstrong

Decision theory is back in fashion (defining fashion as "one good post on a good EA blog"). Bentham's Bulldog (BB) has published a case against FDT (functional decision theory), contrasting rationalist enthusiasm with academic scepticism: "Academic decision theorists don't like the theory. The number of academic decision theorists who adopt it could be counted on one hand by someone missing four of their fingers." I am, just barely, a published academic decision theorist, so you can keep a small finger to count me too. My position is that, though FDT may have problems with its definitions and under-definedness, we can build defined variants that achieve what FDT attempted to. I want to do two things in this post. First, sketch a "pragmatic" version of FDT designed to sidestep the theoretical pitfalls that Will MacAskill and Wolfgang Schwarz identify. Second, take a closer look at what predictors actually do, and argue that whenever they make counterfactual predictions, decision theory shades into game theory -- which explains why EDT/TDT/UDT/FDT can look irrational in the odd branch. It's the old debate of "should you pay the blackmailer", dressed up in predictor garb. Pragmatic FDT MacAskill and BB both [...] ---Outline:(01:26) Pragmatic FDT(05:54) Exploitable isomorphisms(07:10) How we identify likely-true isomorphisms(10:27) Application to standard problems(12:00) Discontinuity across a spectrum of predictors(15:05) No advanced counterpossible theory required(15:30) Predictors, counterfactuals, and game theory(19:47) Conclusion(21:10) Appendix: CDT can't believe in predictors The original text contained 10 footnotes which were omitted from this narration. --- First published: July 3rd, 2026 Source: https://www.lesswrong.com/posts/SdGbWkCZgCN7EGBxM/pragmatic-fdt-and-predictors-as-game-theory-1 --- Narrated by TYPE III AUDIO.