The counting and classifying of story lines is a venerable literary pastime, one that has occasionally proved so strenuous and competitive that it could pass among book people for sport. For good reason. Any tally of possible plots risks bumping up against what for fiction writers is the cornerstone of the profession: the claim to originality. Long a sensitive issue, it has become only more fraught with the advent of A.I. and the proliferation of chatbots able to generate “new” stories derived entirely from troves of old ones, all without the aid of an author.

Aristotle made the first stab at a plot count around 330 B.C., when he declared that there were just two kinds of stories: simple (featuring a change in fortune) and complex (in which the change in fortune is accompanied by setbacks and reversals — for Aristotle, the perfect tragedy).

Two millenniums later, the count had swelled. In 1892, Rudyard Kipling suggested that the number of plots was actually 69, a high-water mark for sure, but then Kipling had witnessed the novel’s spectacular efflorescence over the course of the preceding century. Still, he floated the claim in a few lines of Victorian doggerel, so it’s possible he intended it partly in jest.

In any case, it didn’t stick. Over the next 100 years, the number ticked steadily downward, from 36, the figure touted in an 1895 book by the Frenchman Georges Polti (who credited it to Goethe, who in turn had gotten it from an 18th-century Italian), to 20, the figure championed in 1993 by the American Ronald Tobias, in his book “20 Master Plots: And How to Build Them.” Tobias gave his prior tabulators a gracious nod (“all of these answers are right to some degree,” he allowed), but in his view the “20 master plots” — from “quest” and “adventure” to “underdog,” “forbidden love” and, my favorite, “wretched excess” — covered the bases.

Then, in 2004, Christopher Booker, a founder of the British satirical magazine Private Eye who claimed to have devoted more than 30 years to the issue, published “The Seven Basic Plots,” delineating the handful of story lines he believed undergird everything from “Beowulf” to “Jaws,” P.G. Wodehouse to Proust, and the Marquis de Sade to “The Texas Chain Saw Massacre.” It presumably didn’t hurt his case that the number seven has a connotation, dating at least to the Bible, of divine perfection. In Booker’s account, the most impressive stories were those that managed to squeeze all seven plots into a single tale. “The Lord of the Rings” had them all: the quest, vanquishing the monster, rags to riches, voyage and return, comedy, tragedy and rebirth.

But seven, too, was not destined to last. In 2016, data scientists at the University of Vermont, exploiting advances in natural language processing, plugged 1,737 stories scraped from the Project Gutenberg website into a software program in order to chart their “emotional arcs.” Their custom “hedonometer” examined each story in blocks of 10,000 words, assigning a “meaningful sentiment score” to every chunk, and allowing the researchers to express the results as a series of nifty graphs. The one for “Harry Potter and the Deathly Hallows” shows a mountain range of peaks and valleys, ending, after Voldemort is finally killed, on a steep upward incline toward a summit at happily ever after. The study made news: The world’s stories boiled down to “six basic shapes.”

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