Let's Discuss Functional Decision Theory

Nate says: "The main datapoint that Rob left out: one reason we don't call it UDT (or cite Wei Dai much) is that Wei Dai doesn't endorse FDT's focus on causal-graph-style counterpossible reasoning; IIRC he's holding out for an approach to counterpossible reasoning that falls out of evidential-style conditioning on a logically uncertain distribution. (FWIW I tried to make the formalization we chose in the paper general enough to technically include that possibility, though Wei and I disagree here and that's definitely not where the paper put its emphasis. I don't want to put words in Wei Dai's mouth, but IIRC, this is also a reason Wei Dai declined to be listed as a co-author.)"

I actually think it's a downgrade. It doesn't include the fix that Wei calls UDT1.1 [LW · GW], quantifying over all possible observation-action maps, instead of quantifying over possible actions for the observation you've actually received. The FDT paper has a footnote saying the fix would only matter for multi-agent problems, which is wrong. All my posts about UDT assume the fix as a matter of common sense.

It has on the page 2: "Ideas reminiscent of FDT have been explored by many, including Spohn (2012), Meacham (2010), Yudkowsky (2010), Dai (2009), Drescher (2006), and Gauthier (1994)."

My model is that 'FDT' is used in the paper instead of 'UDT' because:

• The name 'UDT' seemed less likely to catch on.
• The term 'UDT' (and 'modifier+UDT') had come to refer to a bunch of very different things over the years. 'UDT 1.1' is a lot less ambiguous, since people are less likely to think that you're talking about an umbrella category encompassing all the 'modifier+UDT' terms; but it's a bit of a mouthful.
• I've heard someone describe 'UDT' as "FDT + a theory of anthropics" -- i.e., it builds in the core idea of what we're calling "FDT" ("choose by imagining that your (fixed) decision function takes on different logical outputs"), plus a view to the effect that decisions+probutilities [LW · GW] are what matter, and subjective expectations don't make sense. Having a name for the FDT part of the view seems useful for evaluating the subclaims separately.

The FDT paper introduces the FDT/UDT concept in more CDT-ish terms (for ease of exposition), so I think some people have also started using 'FDT' to mean something like 'variants of UDT that are more CDT-ish', which is confusing given that FDT was originally meant to refer to the superset/family of UDT-ish views. Maybe that suggests that researchers feel more of a need for new narrow terms to fill gaps, since it's less often necessary in the trenches to crisply refer to the superset.

I read it several months ago and was wondering the same thing. Although it's more than a branding change, FDT is much clearer put and much easier to understand.

Thanks heaps, that really makes it much less confusing!