TITLE: Recursion, Natural Language, and Culture AUTHOR: Eugene Wallingford DATE: July 04, 2007 9:19 PM DESC: ----- BODY: M.C. Escher, 'Hands' It's not often that one can be reading a popular magazine, even one aimed at an educated audience, and run across a serious discussion of recursion. Thanks to my friend Joe Bergin for pointing me to The Interpreter, a recent article in the The New Yorker by Reporter at Large John Colapinto. The article tells the story of the Pirahã, a native tribe in Brazil with a most peculiar culture and a correspondingly unusual language. You see, while we often observe recursion in nature, one of the places we expect to see it is in natural language -- in the embedding of sentence-like structures within other sentences. But the Pirahã don't use recursion in their language, because their world view makes abstract structure meaningless. Though recursion plays a critical role in Colapinto's article, it is really about recursion; it is about a possible crack in Chomsky's universal grammar hypothesis about language, and some of the personalities and technical issues involved. Dan Everett is a linguist who has been working with the Pirahã since the 1970s. He wrote his doctoral dissertation on how the Pirahã language fit into the Chomsky, but upon further study and a new insight now "believes that Pirahã undermines Noam Chomsky's idea of a universal grammar." As you might imagine, Chomsky and his disciples disagree. What little I learned about the Pirahã language makes me wonder at what it must be like to learn it -- or try to. One the one hand, it's a small language, with only eight consonants and three vowels. But that's just the beginning of its simplicity:
The Pirahã, Everett wrote, have no numbers, no fixed color terms, no perfect tense, no deep memory, no tradition of art or drawing, and no words for 'all', 'each', 'every', 'most', or 'few' -- terms of quantification believed by some linguists to be among the common building blocks of human cognition. Everett's most explosive claim, however, was that Pirahã displays no evidence of recursion, a linguistic operation that consists of inserting one phrase inside another of the same type..."
This language makes Scheme look like Ada! Of course, Scheme is built on recursion, and Everett's claim that the Pirahã don't use it -- can't, culturally -- is what rankles many linguists the most. Chomsky has built the most widely accepted model of language understanding on the premise that "To come to know a human language would be an extraordinary intellectual achievement for a creature not specifically designed to accomplish this task." And at the center of this model is "the capacity to generate unlimited meaning by placing one thought inside another", what Chomsky calls "the infinite use of finite means", after the nineteenth-century German linguist Wilhelm von Humboldt.
According to Everett, however, the Pirahã do not use recursion to insert phrases one inside another. Instead, they state thoughts in discrete units. When I asked Everett if the Pirahã could say, in their language, "I saw the dog that was down by the river get bitten by a snake", he said, "No. They would have to say, 'I saw the dog. The dog was at the beach. A snake bit the dog.'" Everett explained that because the Pirahã accept as real only that which they observe, their speech consists only of direct assertions ("The dog was at the beach."), and he maintains that embedded clauses ("that was down by the river") are not assertions but supporting, quantifying, or qualifying information -- in other words, abstractions.
The notion of recursion as abstraction is natural to us programmers, because inductive definitions are by their nature abstractions over the sets they describe. But I had never before thought of recursion as a form of qualification. When presented in the form of an English sentence such as "I saw the dog that was down by the river get bitten by a snake", it makes perfect sense. I'll need to think about whether it makes sense in a useful for my programs. Here is one more extended passage from the article, which discusses an idea from Herb Simon, which appears in the latest edition of the Simon book I mentioned in my last entry:
In his article, Everett argued that recursion is primarily a cognitive, not a linguistic, trait. He cited an influential 1962 article, "The Architecture of Complexity," by Herbert Simon, a Nobel Prize-winning economist, cognitive psychologist, and computer scientist, who asserted that embedding entities within like entities (in a recursive tree structure of the type central to Chomskyan linguistics) is simply how people naturally organize information. ... Simon argues that this is essential to the way humans organize information and is found in all human intelligence systems. If Simon is correct, there doesn't need to be any specific linguistic principle for this because it's just general cognition." Or, as Everett sometimes likes to put it: "The ability to put thoughts inside other thoughts is just the way humans are, because we're smarter than other species." Everett says that the Pirahã have this cognitive trait but that it is absent from their syntax because of cultural constraints.
This seems to be a crux in Everett's disagreement with the Chomsky school: Is it sufficient -- even possible -- for the Pirahã to have recursion as a cognitive trait but not as a linguistic trait? For many armchair linguists, the idea that language and thought go hand in hand is almost an axiom. I can certainly think recursively even when my programming language doesn't let me speak recursively. Maybe the Pirahã have an ability to organize their understanding of the world using nested structures (as Simon says they must) without having the syntactic tools for conceiving such structures linguistically (as Everett says they cannot). I found this to be a neat article for more reasons than just its references to recursion. Here are few other ideas that occurred as I read. Science and Faith Experience
At UNICAMP (State Univ. of Campinas in Brazil), in the fall of 1978, Everett discovered Chomsky's theories. "For me, it was another conversion experience," he said.
Everett's first conversion experience happened when he became a Christian in the later 1960s, after meeting his wife-to-be. It was this first conversion that led him to learn linguistics in the first place and work with the Pirahã under the auspices of the Summer Institute of Linguistics, an evangelical organization. He eventually fell away from his faith but remained a linguist. Some scientists might balk at Everett likening his discovery of Chomsky to a religious conversion, but I think he is right on the mark. I know what it's like as a scholar to come upon a new model for viewing the world and feeling as if I am seeing a new world entirely. In grad school, for me it was the generic task theory of Chandrasekaran, which changed how I viewed knowledge systems and foreshadowed my later move into the area of software patterns. It was interesting to read, even briefly, the perspective of someone who had undergone both a religious conversion and a scientific conversion -- and fallen out of both, as his personal experiences created doubts for which his faiths had no answers for him. Science as Objective Obvious, right? No. Everett has reinterpreted data from his doctoral dissertation now that he has shaken the hold of his Chomskyan conversion. Defenders of Chomsky's theory say that Everett's current conclusions are in error, but he now says that
Chomsky's theory necessarily colored his [original] data-gathering and analysis. "'Descriptive work' apart from theory does not exist. We ask the questions that our theories tell us to ask.
Yes. When you want to build generic task models of intelligent behavior, you see the outlines of generic tasks wherever you look. You can tell yourself to remain skeptical, and to use an objective eye, but the mind has its own eye. Science is a descriptive exercise, and how we think shapes what we see and how we describe. Do you see objects or higher-order procedures when you look at a problem to describe or when you conceive a solution? Our brains are remarkable pattern machines and can fall into the spell of a pattern easily. This is true even in a benign or helpful sense, such as what I experienced after reading an article by Bruce Schneier and seeing his ideas in so many places for a week or so. My first post in that thread is here, and the theme spread throughout this blog for at least two weeks thereafter. Intellectually Intimidating Characters
Everett occupied an office next to Chomsky's; he found the famed professor brilliant but withering. "Whenever you try out a theory on someone, there's always some question that you hope they won't ask," Everett said. "That was always the first thing Chomsky would ask.
That is not a fun feeling, and not the best way for a great mind to help other minds grow -- unless used sparingly and skillfully. I've been lucky that most of the intensely bright people I've met have had more respect and politeness --and skill -- to help me come along on the journey, rather than to torch me with their brilliance at every opportunity. Culture Driving Language One of the key lessons we see from the Pirahã is that culture is a powerful force, especially a culture so long isolated from the world and now so closely held. But you can see this phenomenon even in relatively short-term educational and professional habits such as programming styles. I see it when I teach OO to imperative programmers, and when I teach functional programming to imperative OO programmers. (In a functional programming course, the procedural and OO programmers realize just how similar their imperative roots are!) Their culture has trained them not to use the muscles in their minds that rely on the new concepts. But those muscles are there; we just need to exercise them, and build them up so they are as strong as the well-practiced muscles. What Is Really Universal? Hollywood blockbusters, apparently:
That evening, Everett invited the Pirahã to come to his home to watch a movie: Peter Jackson's remake of "King Kong". (Everett had discovered that the tribe loves movies that feature animals.) After nightfall, to the grinding sound of the generator, a crowd of thirty or so Pirahã assembled on benches and on the wooden floor of Everett's [house]. Everett had made popcorn, which he distributed in a large bowl. Then he started the movie, clicking ahead to the scene in which Naomi Watts, reprising Fay Wray's role, is offered as a sacrifice by the tribal people of an unspecified South Seas island. The Pirahã shouted with delight, fear, laughter, and surprise -- and when Kong himself arrived, smashing through the palm trees, pandemonium ensued. Small children, who had been sitting close to the screen, jumped up and scurried into their mothers' laps; the adults laughed and yelled at the screen.
The Pirahã enjoy movies even when the technological setting is outside their direct experience -- and for them, what is outside their direct experience seems outside their imagination. The story reaches home. From their comments, the Pirahã seemed to understand King Kong in much the way we did, and they picked up on cultural clues that did fit into their experience. A good story can do that. Eugene sez, The Interpreter, is worth a read. -----