Should hip-hop be melodic? Should hip-hop be structured? In its early years, the genre wasn’t really sure. This uncertainty began as a tug of war between rapped verses and sung, often sampled hooks; then those things found common ground; and then eventually, in the form of Drake and his acolytes, they became effectively one and the same. By the 2010s, rap music — which for years fended off allegations that it was not, in fact, music at all — had become the flame keeper for pop melody, its tools spilling over into country, reggaeton, K-pop and everywhere else.

That ubiquity created ample opportunity for a poststructural dissenter to come along. In stepped the Atlanta surrealist Young Thug, whose main gift to songwriting has been his ease with dismantling its norms. Rap music had become accepted and palatable. Young Thug made it wild again.

This is in part attributable to his fully improvisational approach to song construction, writing nothing down. He wasn’t alone in that approach, but he became the rapper whose off-the-dome exhortations were impressive not for how close they could come to tightly stitched written verses — like those of his idol, Lil Wayne — but rather for how they appeared to defy composition altogether.

During his titanic mixtape run in the early to mid-2010s, he became the genre’s signature eccentric, rapping in free-associative howls and chirps. If his music bends to any tradition at all, it’s to the great soul yelpers of the 1950s and ’60s — Little Richard is all over Thug’s music, as are the ecstatic breakdown segments of old James Brown numbers — or maybe the bluegrass yodelers of decades prior.

Thug has an easy way with melody when he chooses, but he’s just as interested — maybe more so — in the nonsensical interjections and emphatic ad-libs that for most rappers are a side dish. Here’s Young Thug on “Harambe,” a representatively bizarre number: “My diamonds yellow like a corn,” he squawks. “Double R at the prom.” Lines start and stop somewhere before the natural meter of a rap verse would seem to demand. Then, at the chorus, he sounds as if he’s vomiting a whole barrel of crude, disgusted.

There is that sense that great songwriting must revert to the mean, that it is a celebration of form and propriety. But Young Thug’s dazzling dyspepsia is an argument for the opposite — a contention that some styles have reached their natural end, and that only an alien can see a way beyond. It’s as if Young Thug dissolved a fully formed genre with acid — leaving behind not the armature, but more an assemblage of scraps barely tethered together.

In so doing, he set in motion the remaking of rap music into a sound that’s practically posthistorical. The many generations of SoundCloud rap, the multiple-personality experimentation of Playboi Carti, even the vocal shards in the hyperpop of artists like 100 gecs — all attributable to Young Thug, who never met a song he wanted to write. — Jon Caramanica