I like most of this; it seems like the sort of post that's going to lead to significant improvements in people's overall ability to do collaborative truth-seeking, because it makes concrete and specific recommendations that overall seem useful and sane.
However,
principally because 'double cruxes' are rare in topics where reasonable people differ
disagreements like Xenia's and Yevgeny's, which can be eventually traced to a single underlying consideration, are the exception rather than the rule
and similar make me wish that posts like this would start by getting curious about CFAR's "n" of several hundred, rather than implicitly treating it as irrelevant. We've been teaching double crux at workshops for a couple of years now, and haven't stopped the way we've stopped with other classes and concepts that weren't pulling their weight.
My sense is that the combined number of all of the double-crux-doubters and double-crux-strugglers still does not approach, in magnitude, the number of people who have found double crux moderately-to-very useful and workable and helpful (and, in specific, the number of people who have been surprised to discover that double cruxes do in fact exist and are findable an order of magnitude more often than one would have naively guessed).
It does not distress me to consider that double crux might be imperfect, or even sufficiently broken that it should be thrown out.
It does distress me when claims about its imperfectness or brokenness fail to address the existing large corpus of data about its usefulness. Posts like these seem to me to be biased toward the perspective of people who have tried to pick it up online and piece it together, and to discount the several hundred people who've been taught it at workshops (well over a thousand if you count crash courses at e.g. EA conferences). At the very least, claim that CFAR is lying or that its participants are socially pressured into reporting a falsehood—don't just ignore the data outright.
(Edit: I consider these to be actually reasonable things to posit; I would want them to be posited politely and falsifiably if possible, but I think it's perfectly okay for people to have, as hypotheses, that CFAR's deceiving itself or others, or that people's self-report data is unduly swayed by conformity pressures. The hypotheses themselves seem inoffensive to me, as long as they're investigated soberly instead of tribally.)
=( Sorry for the strength of language, here (I acknowledge and own that I am a bit triggered), but it feels really important to me that we have better epistemic hygiene surrounding this question. The contra double crux argument almost always comes most strongly from people who haven't actually talked to anyone skilled in double crux or haven't actually practiced it in an environment where facilitators and instructors could help them iterate in the moment toward an actually useful set of mental motions.
(And no, those aren't the only people arguing contra double crux. Plenty of actual CFAR grads are represented by posts like the above; plenty of actual CFAR grads struggled and asked for help and still walked away confused, without a useful tool. But as far as I can tell, they are in a plurality, not a majority.)
It seems critical to me that we be the type of community that can distinguish between "none of CFAR's published material is sufficient to teach this technique on its own" and "this technique isn't sufficiently good to keep iterating on." The former is almost trivially true at this point, but that's weak evidence at best for the latter, especially if you take seriously (repeated for emphasis) the fact that CFAR has a higher n on this question than literally anybody else, as far as I know.
Scattered other thoughts:
As far as I can tell, none of the most serious doubters in the previous thread actually stepped up to try out double crux with any of the people who claimed to be skilled and capable in it. I know there was an additional "post disagreements and we'll practice" thread, but that seemed to me to contain low density of doubters giving it a serious try with proficient partners.
Also, the numbered description in the "what mostly happens" is, according to me, something like an 85% overlap for double crux. It is a set of motions that the double crux class and tips point people toward and endorse. So that leaves me in confuséd disagreement with the claim that it is "perhaps possible" for double crux to be twisted around to include them—from my point of view, it already does. Which again points to a problem with the explanation and dissemination of the technique, but not with the core technique itself, as transmitted to real humans over the course of a couple of hours of instruction with facilitators on hand*. This causes me to wonder whether the real crux is the jargon problem that you alluded to near the end, with people being upset because they keep crystallizing specific and inaccurate impressions of what double crux is, doing things that seem better, and getting angry at double crux for not being those better things (when in at least many of the cases, it is, and the problem is one of semantics).
* Speaking of "a couple of hours of instruction with facilitators on hand," I'm also a little sad about what I read as an implicit claim that "well, double crux doesn't work as well as being the sort of philosopher or debater who's spent thousands upon thousands of hours practicing and looking at the nature of truth and argument and has been educated within a solid culture with a long tradition." It seems to me that double crux can take a 1-4 hour investment of time and attention and jumpstart people to being something like a quarter as good as those lifelong philosophers.
And I think that's amazing, and super promising, and that it's disingenuous to point at literal world-class professionals and say "what they do is better." It strikes me as true, but irrelevant? It's like if I offered an afternoon martial arts seminar that had 50% of its participants walking away with blue-belt level skill (and the other 50% admittedly lost or confused or unimpressed) and someone criticized it for not being as useful or correct as what black belts with ten years of experience do. It's still an afternoon seminar to get excited about, and for outsiders looking in to wonder "what's the secret sauce?"
(I realize now that I'm making a claim that may not have been published before, about double crux being intended to be a scrappy small-scale bootstrapping technique, and not necessarily the final step in one's productive-disagreement evolution. That's a novel claim, and one that other CFAR staff might disagree with me on, so I retract the part of my grrrr that was based on you not-taking-into-account-this-thing-you-couldn't-possibly-have-known-about).
Here's my sense of the bar that putative double crux replacement needs to meet, because I claim double crux is already reliably meeting it:
Be explainable within 30-60 minutes in a deliberately scaffolded educational context
Be meaningfully practicable within another 30-60 minutes
Be sticky enough that people in fact desire to reference it and spread it and use it in the future
Provide a significant boost in productivity-in-debate and/or a corresponding significant reduction in wasted time/antagonism à la giving people 5-25% of the skill that you see in those philosophers
Do all of the above for greater than 33% of people who try it
Here's my sense of what is unfairly and inaccurately being expected of double crux:
Be grokkable by people based entirely on text and hearsay/be immune to problems that arise from [games of telephone] or [imperfect capture and reconstruction through writing].
Be "attractive" in the sense that people fumbling around on their own will necessarily find themselves moving closer toward the right motions rather than sideways or away, without help or guidance.
Be "complete" in the sense that it contains all of of what we know about how to improve disagreement and/or debate.
Provide an efficacy boost of greater than 50% for greater than 75% of the people who try it.
Here are my "cruxes" on this question:
I would drastically reduce my support for double crux as a technique if it turned out that what was needed was something that could be asynchronously transmitted (e.g. because in-person instruction insufficiently scales).
I would drastically reduce my support for double crux if it turned out that 50+% of the people who reported valuable experiences in my presence later on discovered that the knowledge didn't stick or that the feeling had been ephemeral (e.g. possibly social-conformity based rather than real).
I would drastically reduce my support for double crux if I attempted to convey my True Scotsman version to four high-quality skeptics/doubters (such as Thrasymachus) and all four afterward told me that all of the nuance I thought I was adding was non-useful, or had already been a part of their model and was non-novel.
I would drastically reduce my support for double crux if a concrete alternative that was chunkable, grokkable, teachable, and had thing-nature (as opposed to being a set of principles that are hard to operationalize) was proposed and was promising after its first iterations with 30+ people.
tl;dr I claim that most of the good things you point at are, in fact, reasonably captured by double crux and have been all along; I claim that most of the bad things you point at are either due to insufficient pedagogy (our fault) or are likely to be universal and bad for any attempt to create a technique in this space. I recognize that I'm in danger of sliding into No True Scotsman territory and I nevertheless stick to my claim based on having done this with hundreds of people, which is something most others have not had the opportunity to do.
Thank you for your gracious reply. I interpret a couple of overarching themes in which I would like to frame my own: the first is the 'performance issue' (i.e. 'How good is double crux at resolving disagreement/getting closer to the truth'); the second the 'pedagogical issue' (i.e. 'how good is double crux at the second order task of getting people better at resolving disagreement/getting closer to the truth'). I now better understand you take the main support from double crux to draw upon the latter issue, but I... (read more)
Summary: CFAR proposes double crux as a method to resolve disagreement: instead of arguing over some belief B, one should look for a crux (C) which underlies it, such that if either party changed their mind over C, they would change their mind about B.
I don't think double crux is that helpful, principally because 'double cruxes' are rare in topics where reasonable people differ (and they can be asymmetric, be about a considerations strength rather than direction, and so on). I suggest this may diagnose the difficulty others have noted in getting double crux to 'work'. Good philosophers seem to do much better than double cruxing using different approaches.
I aver the strengths of double crux are primarily other epistemic virtues, pre-requisite for double crux, which are conflated with double cruxing itself (e.g. it is good to have a collaborative rather than combative mindset when disagreeing). Conditional on having this pre-requisite set of epistemic virtues, double cruxing does not add further benefit, and is probably inferior to other means of discussion exemplified by good philosophers. I recommend we look elsewhere.
What is a crux?
From Sabien's exposition, a crux for some belief B is another belief C which if one changed one's mind about C, one would change one's mind about B. The original example was the impact of school uniforms concealing unhelpful class distinctions being a crux for whether one supports or opposes school uniforms.
A double crux is a particular case where two people disagree over B and have the same crux, albeit going in opposite directions. Say if Xenia believes B (because she believes C) and Yevgeny disbelieves B (because he does not believe C), then if Xenia stopped believing C, she would stop believing B (and thus agree with Yevgeny) and vice-versa.
How common are cruxes (and double cruxes)?
I suggest the main problem facing the 'double crux technique' is that disagreements like Xenia's and Yevgeny's, which can be eventually traced to a single underlying consideration, are the exception rather than the rule. Across most reasonable people on most recondite topics, 'cruxes' are rare, and 'double cruxes' (roughly) exponentially rarer.
For many recondite topics I think about, my credence it in arises from the balance of a variety of considerations pointing in either direction. Thus whether or not I believe 'MIRI is doing good work', 'God exists', or 'The top marginal tax rate in the UK should be higher than its current value' does not rely on a single consideration or argument, but rather its support is distributed over a plethora of issues. Although in some cases undercutting what I take as the most important consideration would push my degree of belief over or under 0.5, in other cases it would not.
Thus if I meet someone else who disagrees with me on (say) whether God exists, it would be remarkable if our disagreement hinges on (for example) the evidential argument of evil, such that if I could persuade them of its soundness they would renounce their faith, and vice versa. Were I persuaded the evidential argument from evil 'didn't work', I expect I would remain fairly sceptical of god's existence; were I to persuade them it 'does work', I would not be surprised if they maintained other evidence nonetheless makes god's existence likely on the total balance of evidence. And so on and so forth for other issues where reasonable people disagree. I suspect a common example would be reasonably close agreement on common information, yet beliefs diverging based on 'priors', comprised of a melange of experiences, gestalts, intuitions, and other pieces of more 'private' evidence.
Auxiliary challenges to double crux
I believe there are other difficulties with double crux, somewhat related to the above:
Crux-asymmetry
As implied above, even in cases where there is a crux C for person X believing B, C may not be a crux for B for person Y, but it might be something else (A?). (Or, more generally, X and Y's set of cruxes are disjoint). A worked example:
Carl Shulman and I disagree about whether MIRI is doing good research (we have money riding on it). I expect if I lose the bet, I'd change my mind substantially about the quality of MIRI's work (i.e. my view would be favourable rather than unfavourable). I don't see this should be symmetrical between Shulman and I. If he lost the bet, he may still have a generally favourable view of MIRI, and a 'crux' for him maybe some other evidence or collection of evidence.
X or Y may simply differ in the resilience of their credence in B, such that one or the other's belief shifts more on being persuaded on a particular consideration. One commoner scenario (intra-EA) would be if one is trying to chase 'hits', one is probably more resilient to subsequent adverse information than the initial steers that suggested a given thing could be hit.
A related issue is when one person believes they are in receipt of a decisive consideration for or against B their interlocutor is unaware of.
'Changing one's mind' around p=0.5 isn't (that) important
In most practical cases, a difference between 1 and 0.51 or 0 and 0.49 is much more important than between 0.49 and 0.51. Thus disagreements over confidence of dis/belief can be more important, even if they may not count as 'changing one's mind': I probably differ more with a 'convinced Atheist' than an a 'doubter who leans slightly towards Theism'.
Many arguments and considerations are abductive, and so lend strength to a particular belief. Thus a similar challenge applies to proposed cruxes - they may regard the strength, rather than direction, of a given consideration. One could imagine the 'crux' between me and the hypothetical convinced Atheist is they think that the evidential problem of evil provides overwhelming disconfirmation for Theism, whilst I think its persuasive, perhaps decisive, but not so it drives reasonable credence in Theism down to near-zero.
Sabien's exposition recognises this, and so suggests one can 'double crux' over varying credences. So in this sample disagreement, the belief is 'Atheism is almost certain', and the crux is 'the evidential argument from evil is overwhelming'. Yet our language for credences is fuzzy, and so what would be a crux for the difference between (say) 'somewhat confident' versus 'almost certain' hard to nail down in a satisfactory inter-subjective way. An alternative where a change of raw credence is 'changing ones mind' entails all considerations we take to support our credence in a given a belief are cruxes.
Intermezzo
I suggest these difficulties may make a good diagnosis for why double cruxing has not always worked well. Anecdata seems to vary from those who have found it helpful to those who haven't seen any benefit (but perhaps leaning towards the latter), and remarks along the lines of wanting to see a public example.
Raemon's subsequent exegesis helpfully distinguishes between the actual double crux technique. and "the overall pattern of behaviour surrounding this Official Double Crux technique". They also offer a long list of considerations around the latter which may be pre-requisite for double cruxing working well (e.g. Social Skills, Actually Changing your Mind, and so on).
I wonder what value double crux really adds, if Raemon's argument is on the right track. If double cruxing requires many (or most) of the pre-requisites suggested, all disagreements conditioned on meeting these pre-requisites will go about as well whether one uses double crux or some other intuitive means of subsequent discussion.
A related concern of mine is a 'castle-and-keep' esque defence of double crux which arises from equivocating between double crux per se and a host of admirable epistemic norms it may rely upon. Thus when defended double crux may transmogrify from "look for some C which if you changed your mind about you'd change your mind about B too" to a large set of incontrovertibly good epistemic practices "It is better to be collaborative rather than combative in discussion, and be willing to change ones mind, (etc.)" Yet even if double cruxing is associated with (or requires) these good practices, it is not a necessary condition for them.
Good philosophers already disagree better than double cruxing
Per Plutarch's remark, any shortcomings in double crux may count for little if it is the 'best we've got'. However, I believe I can not only offer a better approach, but this approach already exists 'in the wild'. I have the fortune of knowing many extraordinary able philosophers, and not only observe their discussions but (as they also have extraordinary reserves of generosity and forbearance) participate in them as well. Their approach seems to do much better than reports of what double cruxing accomplishes.
What roughly happens is something like this:
X and Y realize their credences on some belief B vary considerably.
X and Y both offer what appear (to their lights) the strongest considerations that push them to a higher/lower credence on B.
X and Y attempt to prioritize these considerations by the sensitivity of credence in B is to each of these, via some mix of resilience, degree of disagreement over these considerations, and so forth.
They then discuss these in order of priority, moving topics when the likely yield drops below the next candidate with some underlying constraint on time.
This approach seems to avoid the 'in theory' objections I raise against double crux above. It seems to avoid some of the 'in practice' problems people observe:
These discussions often occur (in fencing terms) at double time, and thus one tends not to flounder trying to find 'double-cruxy' issues. Atheist may engage Theist on attempting to undermine the free will defence to the argument from evil, whilst Theist may engage Atheist on the deficiencies of moral-antirealism to prepare ground for a moral argument for the existence of god. These may be crux-y but they may be highly assymetrical. Atheist may be a compatibilist but grant libertarian free will for the sake of argument, for example: thus Atheist's credence in God will change little even if persuaded the free will defence broadly 'checks out' if one grants libertarian free will, and vice versa.
These discussions seldom get bogged down in fundamental disagreements. Although Deontologist and Utilitarian recognise their view on normative ethics is often a 'double crux' for many applied ethics questions (e.g. Euthanasia), they mutually recognise their overall view on normative ethics will likely be sufficiently resilient such that either of them 'changing their mind' based on a conversation is low. Instead they turn their focus to other matters which are less resilient, and thus they anticipate a greater likelihood of someone or other changing their mind.
There appears to be more realistic expectations about the result. If Utilitarian and Deontologist do discuss the merits of utilitarianism versus (say) kantianism, there's little expectation of 'resolving their disagreement' or that they will find or mutually crucial considerations. Rather they pick at a particular leading consideration on either side and see whether it may change their confidence (this is broadly reflected in the philosophical literature: papers tend to concern particular arguments or considerations, rather then offering all things considered determinations of broad recondite philosophical positions).
There appear to be better stopping rules. On the numerous occasions where I'm not aware of a particularly important consideration, it often seems a better use of everyone's time for me to read about this in the relevant literature rather than continuing to discuss (I'd guess 'reading a book' beats 'discussing with someone you disagree with' on getting more accurate beliefs about a topic per unit time surprisingly often).
Coda: Wherefore double crux?
It is perhaps possible for double crux to be expanded or altered to capture the form of discussion I point to above, and perhaps one can recast all the beneficial characteristics I suggest in double crux verbiage. Yet such a program appears a fool's errand: the core of the idea of double crux introduced at the top of the post is distinct from generally laudable epistemic norms (c.f. Intermezzo, supra), but also the practices of the elite cognisers I point towards in the section above. A concept of double crux so altered to incorporate these things is epiphenomenal - the engine which is driving the better disagreement is simply those other principles and practices double crux has now appropriated, and its chief result is to add terminological overhead, and, perhaps, inapt approximation.
I generally think the rationalist community already labours under too much bloated jargon: words and phrases which are hard for outsiders to understand, and yet do not encode particularly hard or deep concepts. I'd advise against further additions to the lexicon. 'Look for key considerations' captures the key motivation for double crux better than 'double crux' itself, and its meaning is clear.
The practices of exceptional philosophers set a high bar: these are people selected for, and who practice heavily, argument and disagreement. It is almost conceivable that they are better than this than even the rationalist community, notwithstanding the vast and irrefragable evidence of this group's excellence across so many domains. Double crux could still have pedagogical value: it might be a technique which cultivates better epistemic practices, even if those who enjoy excellent epistemic practices have a better alternative. Yet this does not seem the original intent, nor does there appear much evidence of this benefit.
In the introduction to double crux, Sabien wrote that the core concept was 'fairly settled'. In conclusion he writes:
I respectfully disagree. I see considerable flaws in double crux, which I don't think have much prospect of adequate repair. Would that time and effort be spent better looking elsewhere.