Transitivity and its failures.

In life, we tend to expect transitivity. In other words: if A > B, and B > C, then A > C.

A jackal is heavier than a cobra. A cobra is heavier than a mongoose. So a jackal had better outweigh a mongoose, or else some weight-conscious animal has been editing brazen lies onto Wikipedia.

But weight is simple. A single measurement. Complex traits—like, say, fighting ability—can’t be so easily summarized. You’ve got to consider speed, strength, strategy, tooth sharpness, poison resistance, endorsement deals… with so many interacting factors, transitivity fails. In this case, a mongoose can defeat a cobra, which can defeat a jackal, which can defeat a mongoose.

The same is true of human combat: in a trio of famous fights, Joe Frazier beat Muhammad Ali, who beat George Foreman, who beat Joe Frazier.

You find a similar dynamic in another facet of everyday life. That’s right: the mating strategies of the male side-blotched lizard.

Some males (“monogamists”) stick close to a single mate. But they’re outcompeted by another kind (“aggressors”) who conquer a large territory, building a harem of many mates. Aggressors, too, have a weakness: a third kind of male (“sneakers”) who wait until the aggressor is away, then get busy with his unprotected mates. Yet the sneaker, in turn, cannot succeed against the watchful monogamist. Aggressor conquers Monogamist, who defends against Sneaker, who gets the better of Aggressor.

Next time someone proposes a game of Rock, Paper, Scissors, I urge you to counter-propose with a game of Lizard, Lizard, Lizard.

Political scientists boast their own version of non-transitivity: the Condorcet Paradox. In an election with multiple choices, it’s possible that the electorate will prefer Taft to Wilson, Wilson to Roosevelt, and Roosevelt to Taft. More than just another great a Rocks, Paper, Scissors replacement, this is a vexing challenge for political theorists. It means that seemingly innocent changes to the structure of an election may have dramatic effects on its outcome.

Indulge me one more example, a favorite of mathematicians. You place three special dice on the table for inspection, and allow your opponent to pick whichever one they want. You then pick one of the remaining two. Both dice are rolled, and the highest number wins.

The trick? Their strength is non-transitive. A usually beats B, which usually beats C, which usually beats A.

Whoever picks their die second can always seize the advantage.

Cool fact about this particular trio: If you bring out a second die of each kind, and compete by rolling a pair of same-color dice, then the cycle reverses direction.

As we’ve seen, transitivity holds in the simplest cases (6 > 5, and 5 > 4, so 6 > 4) but wilts under the breath of complexity. I’m afraid to report that real life is rather complex. Every decision we make could lead to a dizzying array of outcomes: some good, some bad, some likely, some not, and all of them contingent on forces beyond our control.

In one psychology study, students were asked to choose between pairs of fictional job applicants. Their preferences formed a non-transitive loop: A beat B, who beat C, who beat D, who beat E, who beat A. “I must have made a mistake somewhere,” one student fretted, when shown the non-transitivity of his choices. He hadn’t.

It’s just that transitivity is simple, and making decisions under uncertainty is not.

These thoughts circle my head any time I’m asked to rank anything. Sure, our world permits occasional clarity. The best gymnast is Simone Biles. The best Billy Joel album is “The Stranger.” The best squash to eat—not to mention to pronounce—is “butternut.”

But usually it’s not so simple. What’s your favorite Le Croix flavor? Who is the strongest student in your class? What writer has inspired and/or depressed you most? In such cases, there may be no right answer, just a non-transitive mess.

8 thoughts on “Transitivity and its failures.

  1. Perhaps it can be of interest that mechanical toys (e.g. intransitive monkeys, combs, gears etc) are possible as well. They are related to the paradox of intransitive voting by Condorcet (https://en.wikipedia.org/wiki/Condorcet_paradox) and cellular automata
    https://nkj-ru.translate.goog/archive/articles/43663/?_x_tr_sl=ru&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp
    (Original text: https://www.nkj.ru/archive/articles/43663/)

  2. I love the moral here of humility in the face of complexity. I do think it’s worth emphasizing, though, that an individual acting rationally cannot have cyclic preferences (see https://www.wikiwand.com/en/Money_pump). So when there’s ranking to be done and intransitivity pops up, I think that’s best taken as a cue to look out for moving goalposts; that is, it might be that every option was not evaluated under the same criterion, but that does not mean that transitivity would still make sense if a common criterion were being used. For example, if Frazier, Ali, and Foreman, all beat each other in a 3-cycle, the thing to realize is that Frazier is strictly better than Foreman at the task of “boxing against Muhammad Ali”, while Ali is better than Frazier at “boxing against George Foreman” and Foreman is better than Ali at “boxing against Joe Frazier;” these are three distinct tasks.

    Of course, the lesson when this pattern emerges does not have to be “darn, let’s throw out that information and hunt for a well-specified criterion now” – it could be that there’s just more complexity to your original question than you realized, and it’s best to embrace that rather than try to work around it. If you’re putting together the U.S. Olympic boxing team, to keep up the same example, the takeaway probably shouldn’t be to ignore head-to-head results and have each athlete’s punching force measured so you have an easily quantitative, transitive way of ranking them. Instead, it’s probably that there are many different kinds of boxing match-ups, a good thing to keep in mind as you try to come up with the much more difficult “all things considered” way to rank your choices. Ultimately, though, if you have to choose, you will need to rank them, and that ranking can’t be transitive.

    So, basically, I DO think the student in the job application study made a mistake, because his head-to-head comparisons of candidate A to candidate B, and candidate B to candidate C, etc. clearly weren’t based on a standard metric of applicant quality that would allow him to rank them in order. I’m not saying there aren’t real head-to-head scenarios you could put job applicants in where the winners form a non-transitive loop – maybe, if you asked them to debate each other, this would happen, which would be a good prompt for realizing how complex and varied the task of debating is. But I AM saying that using those head-to-head results to do a ranking, and ending up with a non-transitive loop, is nonsensical (and in fact would make it impossible to actually choose an applicant).

    1. Thanks for the thoughtful reply! I love your decomposition of the boxing triangle into three distinct tasks. This was a good challenge to my thinking.

      Having chewed on it a little, I’ve got a thought on why, in complex scenarios, goalpost-moving may be unavoidable.

      Say we’re choosing an assistant professor at a liberal arts college. A is an award-winning researcher whose undergrads often publish; B is an award-winning teacher whose textbook is used nationwide; and C is an award-winning mentor with a track record of helping first-generation college students. Who do we pick?

      The goal of a liberal arts college is something like “help our students thrive academically.” But which students? Those eyeing grad school (i.e., our top performers) may benefit most from A. The most vulnerable ones, at risk of not finishing their degrees, may benefit most from C. And the students in between, likely to graduate but unlikely to become academics, may benefit most from the rigorous instruction of B. That’s not to mention all the different things that “academic thriving” could entail: independent thought, disciplinary knowledge, intellectual curiosity, etc. In other words, our goal is not singular or simple; it’s highly multi-dimensional. In a strict sense, rank-ordering is impossible.

      Of course, “A, B, and C cannot be ranked” is different from “A > B > C > A.” The latter seems clearly irrational. So how do we wind up with non-transitive loops?

      To compare a pair of candidates, we need to project our complex goals down into a single dimension. There is no correct or best way to do this. Different pairs of candidates may induce different projections – especially because we will try to pick projections that make each decision clearer and easier. For example, we may say “B > A, because B will help more of our students.” Then we may say, “C > B, because helping our first-gen students is an urgent priority right now.” And then we may say, “A > C, because at institution of higher learning, we’d be crazy to pass on a top-tier researcher.” In each case, we select a criterion that makes the pairwise comparison easy. After all, it’d be silly to choose a criterion on which they come out tied!

      Anyway, that’s why I see goalpost-moving as not necessarily irrational. Instead, it’s a consequence of repeatedly projecting multi-dimensional goals down to a single-dimensional criterion, and rationally choosing the most convenient projection each time.

      (Why not pick the projection in advance, at the beginning of the hiring process? This would avoid non-transitive loops, but might also make the decision harder than necessary, or lead to a choice that doesn’t “feel” right or satisfying. So again, whether this is a good idea depends on how you boil down the multi-dimensional goals of a hiring process into a single criterion!)

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