The Ghost's Vocabulary

How the computer listens for Shakespeare's "voiceprint"

In 1842 literature and science met with a thud. Alfred Tennyson had just published his poem "The Vision of Sin." Among the appreciative letters he received was one from Charles Babbage, the mathematician and inventor who is known today as the father of the computer. Babbage wrote to suggest a correction to Tennyson's "otherwise beautiful" poem—in particular to the lines "Every moment dies a man, /Every moment one is born."

"It must be manifest," Babbage pointed out, "that, were this true, the population of the world would be at a standstill." Since the population was in fact growing slightly, Babbage continued, "I would suggest that in the next edition of your poem you have it read: 'Every moment dies a man,/Every moment 1-1/16 is born.'" Even this was not strictly correct, Babbage conceded, "but I believe 1-1/16 will be sufficiently accurate for poetry."

Today computers are standard tools for amateur and professional literary investigators alike. Shakespeare is both the most celebrated object of this effort and the most common. At Claremont McKenna College, in California, for example, two highly regarded faculty members have devoted years of their lives to a computer-based attempt to find out whether Shakespeare, rather than Francis Bacon or the Earl of Oxford or any of a myriad of others, wrote the plays and poems we associate with his name.

As Babbage's venture into criticism foreshadowed, the marriage of computers and literature has been an uneasy one. At the mention of computers or statistics, many Shakespeareans and others in the literary establishment wrinkle their noses in distaste. To approach the glories of literature in this plodding way is misguided, they say, and misses the point in the same way as does the oft-cited remark that the human body is worth just a few dollars—the market value of the various chemicals of which it is composed. "This is just madness," says Ricardo Quinones, the chairman of the literature department at Claremont McKenna. "Why don't they simply read the plays?"

Rather than read, these literary sleuths prefer to count. Their strategy is straightforward. Most are in search of a statistical fingerprint, a reliable and objective mark of identity unique to a given author. Every writer will sooner or later reveal himself, they contend, by quirks of style that may be too subtle for the eye to note but are well within the computer's power to identify.

For a University of Chicago statistician named Ronald Thisted, the call to enter this quasi-literary enterprise came on a Sunday morning in December of 1985. Thisted had settled down with The New York Times Book Review and an article by Gary Taylor, a Shakespeare scholar, caught his eye. Taylor claimed that he had found a new poem by Shakespeare at Oxford's Bodleian Library. Among the many reasons Taylor advanced for believing in the authenticity of the poem, called "Shall I Die?," Thisted focused on one. "One of his arguments," Thisted says, "was that several words in the poem don't appear previously in Shakespeare. And that was evidence that Shakespeare wrote it. One's first reaction is, that's dumb. If Shakespeare didn't use these words, why would that be evidence that he wrote the poem?" But Taylor's article went on to explain that in practically everything he wrote, Shakespeare used words he hadn't used elsewhere. Thisted conceded the point in his own mind, but raised another objection. "If ALL the words in there were ones that Shakespeare had never used," he thought, "if it were in Sanskrit or something, you'd say, 'No way Shakespeare could have written this.' So there had to be about the right number of new words." That question—how many new words an authentic Shakespeare text should contain—was similar to one that Thisted himself had taken on a decade before. Together with the Stanford statistician Bradley Efron, then his graduate adviser, Thisted had published a paper that proposed a precise answer to the question "How many words did Shakespeare know but never use?" The question sounds ludicrous, like "How many New Year's resolutions have I not yet made?" Nonetheless, Efron and Thisted managed to answer it. They found the crucial insight in a generation-old story, perhaps apocryphal, about an encounter between a mathematician and a butterfly collector.

R. A. Fisher, the statistical guru of his day, had been consulted by a butterfly hunter newly back from Malaysia. The naturalist had caught members of some species once or twice, other species several times, and some species time and time again. Was it worth the expense, the butterfly collector asked, to go back to Malaysia for another season's trapping? Fisher recast the question as a mathematical problem. The collector knew how many species he had seen exactly once, exactly twice, and so on. Now, how many species were out there that he had yet to see? If the collector had many butterflies from each species he had seen, Fisher reasoned, then quite likely he had sampled all the species that were out there. Another hunting trip would be superfluous. But if he had only one or two representatives of most species, then there might be many species yet to find. It would be worth returning to Malaysia. Fisher devised a mathematical way to make that rough idea precise (and reportedly suggested another collecting trip). Efron and Thisted's question was essentially the same.

Where the naturalist had tramped through the rain forest in search of exotic butterflies, the mathematicians could scan Shakespeare in search of unusual words. By counting how many words he used exactly once, exactly twice, and so on, they would attempt to calculate how many words he knew but had yet to use.

Neither Efron nor Thisted had imagined that their statistical sleight of hand could ever be put to a live test. No new work of Shakespeare's had been unearthed for decades. Now Taylor had given them their chance. A new Shakespeare poem, like a new butterfly-collecting trip to the jungle, should yield a certain number of new words, a certain number that Shakespeare had used once before, and so on. If Shakespeare did write "Shall I Die?," which has 429 words, according to the mathematicians' calculations it should have about seven words he never used elsewhere; it has nine. To Efron and Thisted's surprise, the number of words in the poem which Shakespeare had used once before also came close to matching their predictions, as did the number of twice-used words, all the way through to words he had used ninety-nine times before. The poem, which sounds nothing like Shakespeare, fit Shakespeare like a glove.

This is work that can suck up lives. One Defoe scholar, trying to pick out true Defoe from a slew of anonymous and pseudonymous works, has pursued his quarry for twenty years, with no end in sight. A team trying to determine if the Book of Mormon was composed by ancient authors or by the nineteenth-century American Joseph Smith took 10,000 hours to produce a single essay. (The largely Mormon team of researchers concluded that Smith had not written the Book of Mormon. Confirmed samples of Smith's prose, the researchers argued, showed patterns of word usage different from those in the Book of Mormon.) Paper after paper begins with a trumpet fanfare and ends with a plaintive bleat. One writer, for instance, decided to determine whether Jonathan Swift or one of his contemporaries had written a particular article, by pigeonholing his words according to what part of speech they were. "The only positive conclusion from over a year of effort and the coding of over 40,000 words," she lamented, "is that a great deal of further study will be needed." (Swift himself had satirized, in Gulliver's Travels, a professor who had "employed all his Thoughts from his Youth" in making "the strictest Computation of the general Proportion there is in Books between the Numbers of Particles, Nouns, and Verbs, and other Parts of Speech.")

Despite the shortage of triumphs the field is growing, because more and more of the work can be assigned to electronic drudges. Scholars once had to count words by hand. Later they had the option of typing entire books into a computer, so that the machine could do the counting. Today computers are everywhere, and whole libraries of machine-readable texts are available. Software to do deluxe slicing and dicing is easy to obtain.

As a result, everything imaginable is being counted somewhere. Someone at this moment is tallying up commas or meticulously computing adjective-to-adverb ratios. But sophisticated tools don't automatically produce good work. A future Academy of Statistics and Style might take as its motto the warning that the Nobel laureate P. B. Medawar issued to his fellow scientists: "An experiment not worth doing is not worth doing well."

Among those least likely to be fazed by such pronouncements is a professor of political science at Claremont McKenna College named Ward Elliott. Elliott is an authority on voting rights, a cheerful eccentric, and, like his father before him, inclined to view the Earl of Oxford as the true author of Shakespeare's works. Four years ago Elliott recruited Robert Valenza, an expert programmer also on the Claremont McKenna faculty, and the two set to work on the authorship question.

This time the model would be not butterfly hunting but radar. Valenza had spent considerable time devising mathematical procedures to find the patterns obscured by noisy and jumbled electronic signals. Adapted to Shakespeare, the idea was to go beyond counting various words, as many others had done, and see whether consistent patterns could be found in the way certain key words were used together. Two writers might use the words "blue" and "Green" equally often throughout a text, for example, but the writers could be distinguished if one always used them on the same page while the other never used them together.

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