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When Young Thug exploded from Atlanta’s rap underground into national consciousness last year, there were lots of things that set him apart. There was his appearance—a 6’3″ dude in a dress is hard to miss. There was his predilection for addressing his male friends as “bae” and “hubby.” But most obvious to listeners was how hard it was to understand what he was saying. Although Young Thug’s woozy, warbling songs certainly convey his feelings, they don’t fit neatly into a rap formula focusing on intricate—or even intelligible—wordplay.

The result is an infectious sound that makes sing-a-longs and description difficult. In The Rap Year Book, published earlier this week, Grantland writer Shea Serrano takes one side of the debate. “Imagine if you took both of your feet and stuck them in a bucket full of warm mud and wiggled your toes around,” he writes, “except that mud isn’t mud, it’s your soul.” Young Thug has his share of detractors, though; as rapper Hopsin says in the intro of a warble-rap parody he released last week, “these fools ain’t spittin’ no type of dope shit… they’re not even saying words anymore.”

But Young Thug’s music doesn’t leave behind rap’s signature self-expression through wordplay. Instead, he’s the latest step in the genre’s linguistic evolution: Young Thug expresses his feelings more purely through sounds. Rather than explain a social commentary through lyrics, he can leave the layers of analysis to his fans on Instagram and Rap Genius, and use his songs to authentically represent a self.

Serrano sees Young Thug—whom he describes in The Rap Year Book as “maybe the first post-text rapper, in that he doesn’t even really need words”—as part of a progression of emotion, feeling-based rap. If Kanye’s “Say You Will” showed us the steps for emotional transparency in rap, and Drake’s confessional style familiarized us with the moves, the vocal instrumentation and emotional onomatopoeia that is Young Thug came in and started doing some avant garde interpretive dance. The Atlanta rapper, along with contemporaries like Future and Rich Homie Quan, can better express himself without the filter of words. To translate a sense of pure feeling, warble rap turns to sheer sound—a form of communication that linguist Darrin Flynn sees as closer to “spontaneous speech” than rhyming, metaphor-laden poetry.

Warble Rap: A Linguist’s Guide

For linguists, rap songs offer a goldmine of vernacular conversation. “Rap is the largest repository ever of natural black English speech,” explains Flynn, an associate professor of linguistics at the University of Calgary. “The closer that rappers deliver their lines the way they would actually speak around peers, the more it gives you a window into black English vernacular. As a linguist, I get to hear the cadence of how people in Atlanta actually talk with their peers.”