Split and Commit

Duncan Sabien (Deactivated)21 Nov 2021 6:27 UTC
184 points
34 comments7 min readLW link1 review

This is an essay describing a basic sanity-inducing mental movement that I use approximately ten times per week, and suspect other people would benefit from adopting (and regularly reminding each other to do). I’ve talked about it elsewhere, but until now it didn’t have its own linkable reference post.

P1: Things are often not what they seem.

This can be because the seeming itself is broken, e.g. the progression that goes:

“Well, here I am in 1700′s America and it sure seems to me that these black folk are fundamentally intellectually and morally and spiritually inferior to white folk” or “Well, here I am in 1800′s America and it sure seems to me that these women are constitutionally incapable of holding political office” or “Well, here I am in 1900′s America and it sure seems to me that these gay men are an active threat to everyone’s safety, including our women (somehow) and children” or “Well, here I am in 2000′s America and it sure seems to me that ████ ██ ██████ ██ ████ ████████████ █ ███ ██ ██████ ██ ████ █████ ████████ ██ ████ ███ ████ ████ ██████ ███.”

(Or “Well, here I am inventing physics and it sure seems to me that force consistently and exactly equals mass multiplied by acceleration.”)

It can also be because the seeming is generally correct, but there exists variance. If 95% of the marbles in a bag are red, and 5% of the marbles in the bag are green, it’s correct to guess that the next randomly selected marble will be red, because betting on red makes you the least likely to be wrong. But that doesn’t mean that it can’t be green, or that you should be shocked if it’s green. If you bet on red the whole way through the bag, you know you’ll be wrong five percent of the time.

P2: Every observation is evidence in favor of more than one hypothesis.

If my friend tells me my hair looks good, this is an update in favor of my hair looking good and an update in favor of my hair not looking good but my friend lying to me for various reasons (kindness, prank). In order to know which update is larger, you need some other information about what kind of person my friend is, and what our relationship is like.

If I see some breaking news about some person having maybe done something horrible, this is an update in favor of that person having done something horrible, and an update in favor of that person being the target of a smear campaign/​conspiracy, and an update in favor of the presented claim being technically correct but there being a ton of other relevant context and facts that will substantially change the gestalt of the story. In order to know which update is larger, you need some other information, etc.

(Many of my readers will be thinking “this is just Bayes,” and yep, it’s just Bayes.)

The upshot of these two premises is that it’s wise to have at least two active hypotheses running at all times, for any question of import.

By default, it seems to me that most humans have only one, i.e. not a hypothesis at all but a singular belief.

This is true (in my experience) even of the type of person who is acutely aware of their own fallibility, and who acknowledges that they are occasionally (or often) mistaken. Even people who are savvy enough to try to put a number (like “85% confident”) on it, such that they can track their calibration over time, tend to leave the remaining swath of possibility un- or under-specified.

They will admit that they might be wrong in some vague fashion about [free speech, COVID policy, the president, existential risk from artificial intelligence, Kyle Rittenhouse, universal basic income, Leverage Research, the importance of religion, what the person who wrote that comment was obviously really saying, never mind their actual words], etc., but that doesn’t stop them from having only a single real guess in many situations where that seems (to me) to be wildly premature, and an open invitation to all sorts of known and problematic bias.

There’s a huge difference between [having an answer which you are virtuously prepared to abandon, if forced] and [keeping two or more distinct possibilities firmly in focus, even as you track that one of them is substantially more likely than the others].

There’s a difference in how that feels, and there’s a difference in how it influences one’s reactions to new and relevant information. Choosing a single possible world-state and then looking to see if it’s compatible with the available evidence is very different from looking at multiple possible world-states and then asking yourself what sorts of evidence would rule each one out.

To be clear: it’s true that one (often, regrettably) has no choice but to do the equivalent of [placing an unambiguous bet] when it comes to taking actions. Sometimes, you simply have to behave as though the most likely outcome is what’s going to happen—to choose [actions that will pay out if the marble is red, and cost you if the marble is green] over [actions that will pay out if the marble is green, and cost you if the marble is red]. There are many situations where we cannot afford to sit back and do nothing while we wait for more information to come in, and in many of those situations we have to pick a single exclusive strategy and run with it. You can’t always hedge.

But the fact that one must (often, unfortunately) take singular action doesn’t mean that one can’t hold nuanced beliefs. You can put your money on red without losing track of the true fact that the next marble out of the bag could easily be green.

Split and Commit

Here, then, is the recommendation:

When you encounter [evidence] that sure looks to you like it implies [X], then rather than simply switching into “evaluate [X]” mode, you split and commit.


By “split,” I mean that you explicitly ask yourself both:

“What kind of world contains both [evidence] and [X]?”

and also:

“What kind of world contains both [evidence] and [not-X]?”

Don’t just focus on the world where things are what they seem to be, at first blush. Feel free to notice that one possibility seems pretty darn likely, but hold yourself to the standard of seriously and concretely considering at least one other possibility.

“If it turns out that this isn’t what it looks like, what’s the next most likely story that’s still consistent with [evidence]?”


And by “commit,” I mean that you choose a preliminary reasonable-to-you response in each of those possible worlds.

“If this is indeed what it looks like, then I should probably do something like [A]. If it’s not, though, then [A] would be bad/​counterproductive, and I should instead respond with something like [B].”


This commitment doesn’t have to be public. It doesn’t have to be set in stone. It can be conditional, depending on the various possible states of your next piece of evidence.

The key thing is simply that it exist at all. That you set aside the additional thirty seconds it takes to specifically and concretely dignify the possibility that things are not what they currently appear to be, and make a rough draft of what right action looks like, in that world. That you do this habitually, so that in those times when they aren’t what they seemed at first glance, you’re primed to notice, and ready to respond.

Or, if I might embed my tongue firmly in my cheek: if running this algorithm seems to you like a dumb or not-worth-it idea, then fair enough, but...what ought you do in the world where it just looks dumb, and actually isn’t?

Appendix

The following are some responses from people who encountered the split-and-commit tool in earlier essays and had concrete things to say about it.

Rob Bensinger:

A benefit of split-and-commit I’m surprised wasn’t high on your list: people often want to hedge their bets and pick stances and policies that internally feel justified/​OK regardless of what the outcome is—they like being able to strategically switch between ‘that looks bad’ and ‘that is bad’. Split-and-commit makes it easier to catch yourself doing this and discourage anyone from doing it.

Irena Kotíková:

One if my favourite concepts of all time. Especially because I often notice a ton of resistance to keeping the commitment once the split happens.

Marcello Herreshoff:

So the way I see it, it feels more like split and commit has a minimum of three plans. You need the third plan to tell you what experiment to do to figure out which of the two worlds under consideration you live in. Otherwise tomorrow could easily look like “yep; it still seems like things are as they seem, time to execute plan one!”

Logan Strohl:

Immediately after I finished reading this, I practiced the very first step in a training progression for “split and commit” on a walk from my house to the library.

Here’s the exercise I did:

While walking, my attention will happen to land on things. When it does, I’ll run through the following structure: It looks like x. It might instead be that y. If it’s what it looks like, I will p. If y, I will q.

Some examples I happen to remember:

  • It looks like that’s a building. It might instead be an alligator. If it’s what it looks like, I’ll just walk by it. If it’s an alligator, I’ll go get my neighbor to test whether there is in fact a fucking alligator.

  • Seeing that guy from the back, it looks like he’s smoking a cigarette. It might be that he’s not smoking a cigarette. If he is, I’ll walk by him and hold my breath. If he’s not, I’ll walk by him and breathe normally.

  • That looks like a magnolia tree. It might be a tree I’m unfamiliar with. If it’s a magnolia tree, I’ll expect to keep seeing things I associate with magnolia trees if I keep inspecting it. If it’s a tree I’m unfamiliar with, I’ll expect to encounter things I don’t associate with magnolia trees if I keep inspecting it.

Notes on my experience of the walk:

  • Often when I identify an alternative interpretation of some observation, the course of action I commit to is the same in either case, but I come away with a feeling of having learned something anyway.

  • It looks to me like most reasonable responses are expectations of future experiences, rather than physical interventions or policy changes. It may be that this changes when the motion “split and commit” is taken only when I encounter an appropriate trigger, rather than arbitrarily. (I notice myself automatically deciding on courses of action given either state of affairs; yes good.)

  • The one-second version of split and commit involves going back-and-forth two times. The first time you feel the thing you’re seeing from your default perspective, and then flip over to a perspective where you feel its meaning from a different perspective. The second time, you occupy the first perspective while imagining a course of action to take in response, then flip over to the other perspective and imagine an appropriate course of action from there. I started doing the one second version after about seven minutes of practice, which was about three minutes after it became available. I stuck to the slow version for the extra three minutes to make sure I knew what I was doing.

  • There are a lot of alternative interpretations of the same observations, although there may only be a small number that explain the observation about equally well. There is often a moment where I must choose whether to keep generating interpretations. It seems to me from my experience practicing this so far that most of the benefit most of the time comes from identifying a single alternative interpretation, followed by plans of action for each interpretation (although in fact bothering to identify an alternative interpretation is all by itself most of the thing). I have a feeling that there are some kinds of situations where it is wiser to generate several interpretations before committing to courses of action; I will file this under “followup study”, and continue to focus on “split and commit”.

As usual, humans are difficult and complicated and I’m glad I began to practice mostly in their absence, even though this was presented [in its original context] as primarily a social skill. I think focusing on humans should probably be part three of the training progression.

(Part two of the training progression should be to identify and train the triggers for “split and commit”; obviously splitting and committing for absolutely anything my attention happens upon is only useful if I want a rapid-fire training session for the motion itself. The motion is best taken in response to certain kinds of experiences, and the next thing I need to know are which experiences indicate that it’s an especially good time to split and commit.)

Duncan Sabien (Deactivated)21 Nov 2021 6:27 UTC
184 points
34 comments7 min readLW link1 review