What kind of writers are the justices of the Supreme Court? Scalia is reputed for writing trenchantly, Roberts and Kagan with wit, and Kennedy in garrulous and sentimental style. But what do you find if you rigorously analyze the complexity of their vocabularies?

New methods for rigorous textual analysis make it possible to answer this question. In his blog, Matt Daniels, a data scientist, compared the lyrics of 85 rap artists using a method called token analysis. A computer program counts the number of unique words that appear in a text of a given size. For example, the sentence, “The dog chased the cat and then the cat chased the dog,” has 12 words, six of which are unique. Writers who use more unique words write more complexly, with a larger vocabulary. Daniels’ method counts slight variations as unique words—for example, pimps, pimp, pimping, and pimpin’. But a rapper who used pimp over and over would receive a lower score than one who alternated pimp with, say, whoremonger.

Token analysis can yield surprising insights. It turns out that the relatively unknown rappers Dr. Octagon and CunninLynguists use more complex vocabularies than Shakespeare.* And as in so many areas of life, there is a trade-off between artistic merit and commercial success. Daniels quotes Jay Z, who places below the mean, explaining that “I dumbed down for my audience to double my dollars.”

Hip-hop artists and Supreme Court justices may have little in common (aside from their interests in the criminal justice system). But we decided to extend Daniels’ analysis to the justices. In the figure above, we also tossed in five historically famous justices, Shakespeare, and three rappers—DMX, Jay Z, and Aesop Rock. We limited ourselves to the justices’ majority opinions. (More on our code and data here.) Our subjects are arrayed along a line from least to most complex use of vocabulary. The great Chief Justice John Marshall, at the far left, receives a score of 8.7 percent, which means that in 1,000 words of one of his opinions, 87 of his words are unique and the other 913 are repetitions of those words. Justice Oliver Wendell Holmes, at the far right, would use 211 unique words in a 1,000-word text.

Among the current justices, Antonin Scalia uses the most complex vocabulary, exceeding even that of Shakespeare. Last year, he memorably called the majority opinion “legalistic argle-bargle” in United States v. Windsor, one of the gay marriage cases. Kennedy, who is our idea of a bad writer, receives the lowest rating. The others cluster below the mean of the rappers in Daniels’ chart, maybe because they rely on law clerks who are trained in generic law-speak.

Token analysis showcases the kind of great writing that Holmes did (“The common law is not a brooding omnipresence in the sky”). Robert Jackson, a great 20th-century justice best known as the chief U.S. prosecutor at Nuremberg, falls just below Scalia. Consider this line from his opening address to the Nuremberg tribunal:

That four great nations, flushed with victory and stung with injury, stay the hand of vengeance and voluntarily submit their captive enemies to the judgment of the law is one of the most significant tributes that Power has ever paid to Reason.

Not even Aesop Rock could match this level of eloquence.

But not all great justices are great writers. John Marshall, who scores even lower than DMX, was the greatest justice of all time. During his long tenure from 1801–1835, he laid the foundations of the modern Supreme Court, immensely contributing to its power and prestige. But it wasn’t because of his written opinions, which are not eloquent. His most famous line is the unmemorable “We must never forget that it is a constitution we are expounding.” Marshall strengthened the Supreme Court by choosing his battles wisely, and by using his charm and wit to dominate his colleagues. He may have avoided writing flashy opinions so as to avoid drawing attention to his innovations.

Still, four of the five great justices (Holmes, Jackson, Louis Brandeis, and Felix Frankfurter) score higher than the current group aside from Scalia, and we suspect that the pattern would hold if we increased our sample size. Much of the time, in rap and in law, verbal acuity and intellectual depth go hand and hand.

Correction, June 12, 2014: This article originally misidentified rapper Dr. Octagon as Dr. Octagonecologyst. (Return.)

