Can Big Data Clarify the Second Amendment?

What does the Second Amendment mean? This question is at the center of one of the most divisive debates in modern American constitutional law. The amendment itself contains 27 words: “A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.” This provision references both the collective right of a militia and an individual right. Does this two-century-old text, then, mean that Americans today have a right to gun ownership and use?

In a landmark 2008 decision on this question, District of Columbia v. Heller, the Supreme Court was sharply divided. The majority opinion, by Justice Antonin Scalia, concluded, among other things, that the phrase bear arms against would always refer to service in a militia. But bear arms by itself—the wording used in the Second Amendment—could sometimes refer to an individual right. The dissenting opinion, by Justice John Paul Stevens, intimated that the phrase keep and bear arms was a fixed term of art that always referred to militia service.

In the 12 years since that decision, scholars have gained access to a new research tool that some hope can settle this debate: corpus linguistics. This tool allows researchers to search millions of documents to see how words were used during the founding era, and could help courts determine how the Constitution was understood at that time—what is known as “original public meaning.” Corpus linguistics, like any tool, is more useful in some cases than in others. The Second Amendment in particular poses distinct problems for data searches, because it has multiple clauses layered in a complicated grammatical structure.

With that in mind, in mid-2018 we searched large collections of language from around the time of the founding, and published our tentative findings on the Harvard Law Review’s blog. We used two databases: the Corpus of Founding Era American English (COFEA), which contains about 140 million words of text from various American documents published from 1760 to 1799, and the Corpus of Early Modern English (COEME), which covers British English from 1475 to 1800 and includes more than 1 billion words of text. We have now expanded that initial research to consider how other aspects of the Second Amendment were understood at the time of the framing. Our findings show that both Scalia and Stevens appear to have been wrong with respect to at least one of their linguistic claims in the Heller decision.