Too Hot, Too Cold, and Just Right: Why AI Picked Up the Rule of Three and How Humans Can Deal With That

"Rule of three: AI groups ideas in threes to make writing effective, memorable and satisfying."

— Louis Barclay, "Superficial Intelligence: AI Writing"

"Crush your enemies, see them driven before you, and hear the lamentations of their women."

— Conan the Cimmerian, Conan

Not unlike the much-slighted em dash, the rule of three has become a clue that AI wrote text — not definite proof, but enough to raise suspicions. Like the em dash, it shows up because we trained AI on human text (further reading: "The Em Dash: A History of a Mark Nobody Used — Until Everyone Did"). It's giving us what it thinks we want. When it follows the rule of three, though, it's going back further than the sixteenth century, drawing from some of the most basic human concepts.

Here's why we love threes (and why AI does too), and how obvious LLM use differs from solid human construction.

It's a magic number

"Three Is a Magic Number" (Schoolhouse Rock!, 1973)

That song should be firmly lodged in your brain now. You're welcome.

1970s education has something of a point. Threes show up everywhere: the minimum number of angles in a polygon, the minimum points for a flat plane (and thus any structure that stands up on its own), the smallest number of people needed to make a decision without a stalemate, and so on. Three means two sides of an equation and the result, whether that's math or, as in the song, human reproduction.

Three also establishes repeatability — as Fleming's Auric Goldfinger said, "once is happenstance, twice is coincidence, three times is enemy action," and under federal law, a killer isn't "serial" until the third victim (the FBI's working definition has required two victims since 2005). Along those lines, you have to have two matching items to set up a third as different, which is why fairy tales often have three sons on quests or three nights of celebration, and jokes feature a minister, a priest, and a rabbi.

One more thing: three can signify escalation, whether that means the items get larger, more important, or more complicated. Conan's saying fits here, going from simple and direct to a bit abstract and assuming a bunch of things, like that your enemies have women and those women will lament. So does Saint Paul's point about "faith, hope, and charity," if you agree that "the greatest of these is charity."

Three strikes

"Three shall be the number thou shalt count, and the number of the counting shall be three."

— Monty Python and the Holy Grail

"Our three weapons are fear, surprise, and ruthless efficiency... and an almost fanatical devotion to the Pope."

— Monty Python, "Spanish Inquisition" sketch

Now I'm going to contradict myself: most phenomena don't actually come only in threes, or at least not naturally. Sure, you have morning, afternoon, and night... but what about dawn and twilight? Where does "night" start, or "morning," for that matter? A man and a woman may have a little baby, but they may also have twins. Because three is pretty important in math and math-adjacent activities, it also makes a decent categorization system, but all systems have edge cases, blurry lines, and exceptions when dealing with the messiness of life outside math.

Remembering that is one way to distinguish human rule-of-three use from the way it works in AI. Human writers (good ones, at least) turn to triads to make a point or set up a structure, but won't fall back on them all the time. They'll use longer lists or vaguer statements when the situation seems appropriate, or they won't bother grouping ideas at all.

AI doesn't share this discretion. It often uses triads without any particular need to do so. For instance, in the Gettysburg Address, Lincoln says "we can not dedicate — we can not consecrate — we can not hallow — this ground": he's describing successively more intense levels of honor, from the purposeful to the sacred. On the other hand, do you really need to say that a company is "innovative, rule-breaking, and impactful"? Don't "innovative" and "rule-breaking" mean the same thing? (Don't get me started on "impactful," in general.)

Because LLMs don't evaluate the need for the rule of three the way humans do, its simple frequency can be a clue. SlopDetector says more than one triad every 200 words or so is a pretty good sign that there's a machine behind the writing. It's not a hard-and-fast rule, but it helps, particularly if the writing also includes features like corporate phrasing, em dashes, or repetitive sentence structure, all human habits that AI has picked up and inflated.

Next steps

For readers trying to spot AI? Well, once is happenstance, twice is coincidence, and three times means you at least want to do more research. Don't jump to conclusions, though. Neither Conan nor Saint Paul would appreciate being mistaken for a computer. (I'm not sure about Goldfinger.)

For writers? LLM paranoia is going to be a part of life for a while yet, unfortunately, and there will always be those who see AI in every sentence. So it goes: anyone who's been in the business for a while knows that not all readers are reasonable, and they'd find another issue if AI wasn't on the table.

All we can do is our best. With triads, that means slowing down and examining your writing. Ask yourself why you want a group of items and whether there really are three and only three that qualify.

In other words, think about your prose. Whether you're trying to distinguish yourself from AI or not, that can only be a good thing.