“[[[When in the course of human events it becomes necessary for one people [to dissolve the political bands [which have connected them with another]] and [to assume among the powers of the earth, the separate and equal station [to which the laws of Nature and of Nature’s God entitle them]]], a decent respect to the opinions of mankind requires [that they should declare the causes [which impel them to the separation]]].”
—Declaration of Independence, opening sentence
An iconic sentence, this. But how did it ever make its way into the world? At 71 words, it is composed of eight separate clauses, each anchored by its own verb, nested within one another in various arrangements. The main clause (a decent respect to the opinions of mankind requires …) hangs suspended above a 50-word subordinate clause that must first be unfurled. Like an intricate equation, the sentence exudes a mathematical sophistication, turning its face toward infinitude.
To some linguists, Noam Chomsky among them, sentences like these illustrate an essential property of human language. These scientists have argued that recursion, a technique that allows chunks of language such as sentences to be embedded inside each other (with no hard limit on the number of nestings) is a universal human ability, perhaps even the one uniquely human ability that supports language. It’s what allows us to create—literally—an infinite variety of novel sentences out of a limited inventory of words.
But that leads to a curious puzzle: Complex sentences are not ubiquitous among the world’s languages. Many languages have little use for them. They prefer to string together simple clauses. They may even lack certain words such as relative pronouns that and which or connectors like if, despite, and although—these words make it possible to link clauses together into larger sentences. Allegedly, the Pirahã language along the Maici River of Brazil lacks recursion altogether. According to linguist Dan Everett, Pirahã speakers avoid linguistic nesting of all kinds, even in structures such as John’s brother’s house. (Instead, they would say something like: Brother’s house. John has a brother. It is the same one.)
This can’t be pinned on biological evolution. All evidence suggests that humans around the world are born with more or less the same brains. Abundant childhood exposure to a language with layered sentences practically guarantees their mastery. Even adult Pirahã speakers, who have remained unusually isolated from European languages, pick up the trick of complex syntax, provided that they spend enough time interacting with speakers of Brazilian Portuguese, a language that offers an adequate diet of embedded structures.