- If your image of a linguist is of a mild-mannered bookworm quietly pouring over a dusty tome in a secluded study, then you've probably never seen linguists argue over a controversial topic because let me tell you, it can get spicy.

And when it comes to controversial linguistic debates, few are as heated as the theory of universal grammar, commonly known as UG.

The arguments on either side can be mind-numbingly academic, but don't let that fool you.

This is a passionate conflict with each side casting their leaders as epic heroes and their opponents as stodgy relics or narcissistic charlatans.

Perhaps that's because behind all the technical jargon, universal grammar is suggesting something so fundamental about the human experience that like religion or politics, it can feel like a threat or a confirmation of one's entire worldview.

I'm Dr. Erica Brozovsky, and this is "Otherwords."

(bright whimsical music) - [Announcer] "Otherwords."

- There are a lot of characters in this story, but few would disagree that the most central is Noam Chomsky, the linguist and political theorist who's arguably had more impact on the field than any other academic.

Chomsky developed the ideas of universal grammar in the 1950s and 1960s, proposing a theoretical system of syntactic rules that are uniform across all languages and innate to the human mind.

In other words, despite the seeming diversity of languages around the world, everyone is born with the same mental capacity for grammar, which is a product of evolution by natural selection.

Chomsky famously suggested that if an alien visited earth, they think we all spoke the same language with minor regional dialects.

This makes some intuitive sense.

There are, after all, many grammatical features that are found across completely unrelated languages like the distinction between nouns, verbs, and prepositions, or the use of affixes to adjust meaning.

According to Chomsky, UG could explain what he called the poverty of the stimulus.

Generative grammatist like Chomsky have long believed that beneath even the most seemingly simple sentences lurks a deep grammar.

Of such startling computational complexity, it seems impossible that young children could master it so quickly, and with so few examples to learn from, unless the fundamental rules were already hardwired into their brains.

Over the following decades, he refined his theory of universal grammar into something called principles and parameters, which suggested that all languages adhere to a set of concrete principles and variation amongst languages is due to certain parameters being switched on or off, depending on culture, necessity, or random chance.

For instance, all sentences must have a subject, but where that subject is placed in the sentence is a parameter that varies by language.

Chomsky's theories revolutionized the field and became the backbone of linguistic analysis for a generation, but there were still fundamental questions that UG struggled to answer.

For one, if evolution is a slow, gradual process, exactly how does grammar evolve?

Noun's first then verbs.

What part of the brain is responsible for it?

And since the human genome has been largely unchanged for tens of thousands of years, why would a system of expression complex enough to describe particle physics develop amongst the community of simple hunter-gatherers?

Since European languages tended to be overrepresented in linguistic analyses, there were also fears of distorted judgments on what qualified as a universal characteristic.

English grammar, for example, relies heavily on word order, so some accused Chomskians, as they're sometimes called, of overemphasizing it when studying other languages.

Sure enough, as more diverse data rolled in, proponents of UG had to repeatedly revise their lists of principles and parameters to account for unexpected grammatical features of languages like Tagalog, Mandarin, and Warlpiri.

Towards the end of the 20th century, alternative theories that challenged UG started to gain traction like usage-based linguistics, cognitive linguistics, and constructive grammar.

Researchers like Michael Tomasello and Joan Bybee argue that childhood acquisition of language didn't require some mysterious grammar module in the brain, but could be explained by more general cognitive abilities like pattern recognition, frequency gauging and memorization.

Tomasello pointed out the most children's early speech consists of short lists of memorized chunks like gimme or want juice that are repeated for purely functional purposes.

As the vocabulary of chunks grows, they may notice patterns or statistical frequencies that allow them to create their own novel configurations.

And when you think about it, adult speech isn't all that different.

Outside of literature and academic lectures, most of our day-to-day conversations are made up of pretty rote phrases that you've probably heard thousands of times before with little substitutions and alterations here and there.

Do we really think that our brains are doing computational gymnastics under the hood every time we make small talk?

Some even go so far as to suggest that it wasn't until the advent of writing that humans develop the kind of deep grammar that Chomsky and other generative grammatist spend their lives analyzing.

Meanwhile, advancements in brain imaging suggested that there was no centralized language organ, but that the act of speaking was spread across many different parts of the brain, much like other cognitive functions, and despite certain genetic abnormalities having an impact on language, genetic research has failed to find any gene or collection of genes specifically responsible for grammar.

But by this time, UG had become academically entrenched and the majority of linguists were resisted to scrapping the paradigm they had been using their whole careers.

Chomsky himself was known to describe his critics as liars and frauds, and yet around the turn of a century in response to new research and thinking, he refined his theory of UG further into something much simpler and more explicable by evolution.

According to this new theory, at some point in human history, perhaps 50 to 100 thousand years ago, the human brain evolved a unique cognitive ability he called merge.

This allowed us to mentally combine two separate thoughts into a set which we could simultaneously perceived as individual pieces and a united whole.

That set could subsequently be used as an element in another set and so on and so on theoretically without end.

This creates a hierarchical thought structure that would've been useful for things like toolmaking, cooperation, and understanding our environment.

Language, however, is linear.

Our mouths are only capable of saying one word at a time, so in order to translate these hierarchical thoughts into linear sentences, merge developed into grammar.

Essentially, Chomsky distilled all his principles and parameters into one universal characteristic of language, recursion, the nesting of parts of speech into other parts of speech.

For instance, I linearly speak the sentence, Amanda said that while you are out, the green vase you got from your mom fell off the shelf and broke, but the meaning of the sentence is hierarchical with recursive grammar as the intermediary.

According to merge, recursion was a foundation of grammar.

Its true universal element found in all human languages.

In some ways, it was a remarkable concession to his critics.

Not only did he abandon many of his previous claims, he even acknowledged that the mental skill behind grammar may have evolved as a general cognitive ability before later being repurposed for language.

But for some opponents of UG, even merge was too much of an assumption.

In 2005, linguist Daniel Everett claimed to have found a language without recursion.

According to him, the Piraha, an indigenous tribe he'd been living with off and on since the 1970s, did not use embedded clauses.

In English, we can say, Henry says it's raining, with the clause it's raining embed within Henry says X, but this is supposedly forbidden in Piraha.

Perhaps even more controversial was the reason Everett offered for this idiosyncrasy that the Piraha don't talk about anything they haven't personally witnessed, a trait he called the immediacy of experience principle.

Also, supposedly why they lacked stories, deities, and origin myths.

They could say it's raining, but Henry's opinions are pure hearsay, so not worth talking about.

Everett's claims created a firestorm.

Many linguists accused him of misunderstanding UG or Piraha or both.

Some even suggested that Piraha were feeding him a nonsense language.

Chomsky called him a charlatan, and some even suggested his conclusions were racist for suggesting that the Piraha were incapable of abstract thought.

On the less hyperbolic side, a trio of Chomsky and linguists wrote an extensive response to Everett's findings that persuasively argue that Piraha does in fact have clause embedding and cast doubts on the logic of his immediacy of experience principle.

Everett still has his defenders including a glowing biography by novelist Tom Wolfe, but his claims were not the final nail in UG's coffin this some hoped for.

Even the advent of large language models have only given both sides more ammunition.

Opponents of UG say it's proof that a general intelligence can master grammar without a specially designed language organ.

While defenders of UG point out that AI models need to analyze billions of pages of text in order to do so, which seems to bolster Chomsky's poverty of the stimulus theory.

Today, despite all the hoopla, universal grammar is still accepted and taught at linguistic departments around the world.

Surely some of that endurance is due to academic inertia, but it does have several big things going for it.

For one, despite its brain melting complexity, Chomsky's generative grammar remains a cohesive, elegant system that successfully predicts linguistic phenomena in a range of diverse languages.

While alternative theories have certainly gained momentum over the last several decades, no one theory is as detailed or comprehensive.

Also, the uniqueness of language to our species and the universality of it across all members of our species continues to convince many that there must be something biological behind it.

Michael Tomasello argues that the game of chess also has many unique structures, but no one believes that this uniqueness requires an innate chess playing module.

However, very few people can become chess masters, and the vast majority of us need direct instruction to learn it.

But barring some kind of genetic abnormality, every human child becomes a master of grammar before they can even tie their shoes.

Language is an enormous part of what makes us human.

It might be just an emergent technology like bows and arrows or a side effect of other cognitive functions, but it's hard to think of another phenotype in the animal kingdom that is as essential to a species identity without a distinct biological root.

Fish swim, birds fly, humans talk.

Perhaps the debate over UG seems so passionately intractable because its implications go beyond linguistics to the very essence of human nature.

Maybe some people like to think that our behavior is dictated by our biology while others recoil from the idea that our conversations are just repetitions of canned phrases.

Are we products of our genes or our environment, nature or nurture?

Perhaps we'll never know, but we can at least take pride in the fact that what makes the question so difficult to answer is also what makes us so special.