Summary: A Cambist is a manual showing exchange rates of different currencies and measurements. Dutch Booking is when a sequence of trades would leave one party strictly worse off and another strictly better off. Cambist Booking is intended to spark conversation about what priorities or objects you would exchange for each other, and at what rates. 

Tags: Large, Repeatable

Purpose: Taking its title from the excellent short story “The Cambist and Lord Iron,” Cambist Booking is about understanding the idea that everything is, ultimately, trading off against everything else. The extra hour you work earns you a bit of extra money, the money can buy you a coffee so you get up earlier and have an extra hour, you spend that extra hour studying for a better job – but at each step you could have chosen to spend things differently. 

Materials: You need a big stack of cards with things people want written on them, called the Deck. You'll also want a piece of paper and a pen or pencil for each participant, called the Record. 

A workable list of things for the Deck is provided here, along with a PDF for easy printing- just print about ten to a page, single sided, and cut them out. If you want nicer cards, use cardstock like for a business card and the Cambist Booking Back. Regular paper works fine. If you'd rather, you can also handwrite the whole Deck. Feel free to add in your own cards!

Announcement Text: Hello! This event is for general socialization, and also running a game called Cambist Booking. If you’re familiar with the Slate Star Codex post Everything Is Commensurable, or the short story The Cambist and Lord Iron, then this game should sound somewhat familiar to you. It works like this: each person will get a some cards with things you might want on them. You’ll go around asking other people what their cards are, and deciding how to compare the two values – is a sportscar worth more or less than a year’s vacation? Is an hour long massage worth more or less than a new album by your favourite band? We’ll pass out the cards at the start, keeping some in reserve for new arrivals, and spend the time talking about what we value and why. 

Description: Explain the following rules to the audience as you deal out the cards and pencils. Deal one card to each person.

We'll start with a big deck of cards with things people generally like.  Everyone is going to get one card, plus a blank piece of paper and a pencil.  At the top of the blank paper write “Record.” 

Then we're going to mingle, asking each other at what rate we would trade the thing on one of your cards for a thing on the other person’s card. For instance, if I have “A mediocre laptop” and you have “A plane trip anywhere you want” then maybe I think I’d trade two mediocre laptops for one plane trip anywhere I want. I write down, on my Record’s paper, “2 mediocre laptops = 1 plane trip anywhere.” Maybe for you, you’d value a plane trip as worth exactly one laptop, so you would write "1 mediocre laptop = 1 plane trip anywhere" down on your book.  

You can write fractions; for instance if you're comparing "an extra year of life in your current health" to "the ability to breath underwater for a year" you could write "1/4 of an extra year of life in your current health = the ability to breath underwater for a year." Your exchange rate does not have to be the same as your partner's exchange rate. You can also value something negatively; if a card from the Deck offers an hour spent with your parents and you hate spending time with your parents, you might write "1 hour spent with my parents = -$50 USD" to indicate that you would want to be paid fifty dollars to spend an hour with them.

If there's a question of interpretation for a card from the Deck, you and your partner should figure out how you're evaluating it. It's perfectly fine if you interpret a card differently from someone else, as long as you're consistent in how you interpret it.

Then you give your partner your card and they give you theirs, so that you have something new. 

Find someone else and do it again! 

The object of the game is twofold: First, to get as many exchange rates possible. Second, not to get Dutch Booked – that is, never to allow any sequence of exchanges to leave you with less than you started with. For instance, if you’d trade two laptops for one plane ticket, and one plane ticket for one bicycle, but you’d trade one bicycle for one laptop, then you have a problem- Someone could repeatedly trade you bicycles for laptops and laptops for plane tickets in a way that leaves you worse off every time. 

Variations: By default, there's no time limit on discussions and people switch whenever they're done. This is relaxed and easy, but means people can be at loose ends when they separate from their partner and go looking for someone new. If you like, set a regular timer and have everyone switch when the timer goes off. Three minutes is aggressive and quick, twenty minutes will likely have some people finish discussing early. I suggest five to ten minutes is about right.

By default, each discussion is done in pairs. It's easy to tell people to form trios instead of pairs, making their Record line something like "1 plane trip anywhere = the ability to breath underwater for 1/4th of a year = 3 books by your favourite author." This lets people see more card at a time and lets them check if the start and end of their Record line actually match up. It takes more time however.

By default, you deal everyone a single card from the Deck at the start and this forms the cards in circulation for the event. You can deal everyone two or three cards instead, letting them pick their favourite to use. This gives them more options and makes the number of options in circulation larger. It can make it harder to compare all the values someone placed against each other however, since there's no longer guaranteed to be a chain of values. Alternately, you can have people swap out old cards for new ones during the event, perhaps at the halfway mark. If you swap in new cards, I suggest only swapping half the crowd, so that it's likely there will still be comparisons to the old values.

Notes: This could have been called Cambist Arbitrage, but Dutch Booking is accurately describing the thing you do not want to let happen.

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4 comments, sorted by Click to highlight new comments since: Today at 2:17 PM

The activity as described seems to have the following properties:

  • You always keep the cards you were originally dealt and don't trade them for other ones (you just think about and discuss trades). And
  • The trades you think about and discuss are always ones involving the cards you were originally dealt. Therefore,
  • You get inconsistencies if and only if your exchange rates all have the same ratio across the cards you were originally dealt. In particular,
  • If you were originally dealt just one card, there's no opportunity for inconsistency (other than meeting with the same person twice and picking different rates, I guess).

But what the text says about inconsistencies seems like it implies that something different is intended (laptop / plane ticket / bicycle / laptop), and it seems as if this sort of activity might be more interesting if participants sometimes actually swapped cards somehow.

So we could change the rules as follows:

  • Everyone's cards have numbers on, indicating how much/many of the resource in question they own.
  • You can start with all the numbers being 1, or pick them all so that everyone has very handwavily on the order of $1000 worth of each thing, or whatever.
  • If people with cards A and B meet, and their A/B exchange rates differ, then they can pick an exchange rate in the middle (probably ideally the geometric mean, but this isn't a competition and it's fine to pick something near that but easier for calculation) and swap cards as follows: if player 1 has card A with quantity a, and player 2 has card B with quantity b, and the mutually-favourable exchange rate they agree on is that one unit of A is worth r units of B, then after the swap player 1 has card B with quantity ra and player 2 has card A with quantity b/r.
  • When everyone's done with the activity, as well as hoping to have lots of exchange rates recorded and not to have been the victim of a Dutch-book-style cyclic ripoff, everyone looks at what they started with and what they have now and considers whether they do in fact consider themselves better off at the end than at the beginning, and whether they've learned anything interesting about their own priorities from what they ended up with.

[EDITED to add] I see that omark had essentially the same idea and had it first. Leaving this here because my version has more details :-).

[+][comment deleted]10mo20

We ran this in Freiburg, Germany in January 2023 with a total of 10 people.


  • It was very fun!
  • Many people had never explicitly thought about such rates of exchange and they found the implications interesting
  • Some people were able to identify inconsistencies at the end while going over their list of bookings

Worthy of improvement / Unclear things:

  • In the trade I am giving up what I have on my card. Can I give up more than one item? Do I already own that item beforehand? If I am giving up several is it because I own all of them or do I need to get them somehow (e.g. by paying money)? For example if my index card says "An apple" and the other person's index card says "1 million USD", would I trade my single apple for a fraction of the million USD or would I trade many tons of apples for the entire 1 million USD. Do I already own those tons of apples?
    • We solved this by specifying that you own your item once and always trading for a fraction of what the other person owns.
  • Including monetary values like "1 million USD" makes it less fun because those exchange rates are more common anyway
  • Some things are really hard to multiply or subdivide such as "the ability to breathe underwater".
    • We solved this by specifying that the fraction was having this ability for a certain amount of time instead of the rest of your life
  • Since my booking card always compares everything to my own "index card" I don't ever get any obvious inconsistencies. e.g. I only have trades involving the "mediocre laptop" with the plane ticket, with the bicycle, with everything else. But never an exchange between the plane ticket and the bicycle.
    • The inconsistencies only become clear once you start comparing the things on your booking card among themselves, which is made more complicated by the fact that you had to use fractions or multiples in the other trades. It would be great if these inconsistencies become directly obvious as part of the game rules e.g. by trading index cards at some point.

Updated with some of the feedback. The distinction between the Record (where you remember your values) and the Deck (which has things you value written is made clearer. The rules now say to get dealt one card and to trade the cards, so you're always holding something new and your Record is a chained series where you can work through the intermediate steps to compare your start and your end. Also, a couple of variations are introduced.