Memphis, Detroit, New York — in 1965 three record companies held three irreconcilable answers to a single question: how do you make a soul record? Their disagreement would go on to shape the dance floor a decade later.

When people refer to "the soul era," they generally mean the run of records released between roughly 1965 and 1971 by three American labels: Stax in Memphis, Motown in Detroit, and Atlantic in New York. The three operated with very different theories of how to make a soul record, and the difference is what gave each label its sound.

Motown, founded by Berry Gordy in 1959, ran on a Detroit assembly-line logic — the city was the capital of the auto industry, and the label mass-produced hits through division of labor and standardization. Songs were written by a small in-house team — Holland-Dozier-Holland, later Norman Whitfield and others — and recorded by a single house band, the Funk Brothers, who played on virtually every Motown hit cut in Detroit through the 1960s. The result was an extraordinarily consistent sound, finished and bright and engineered for top-40 radio, that put the Supremes, the Temptations, Stevie Wonder, and Marvin Gaye on the same chart as the Beatles.

Stax, in Memphis, ran on the opposite premise. The label's studio was a converted movie theater with a sloped floor, and the house band, Booker T. & the MGs, was racially integrated at a time when that was still controversial in the South. Songs were typically written in the room and tracked live. The Stax sound is grainier than Motown's: drier drums, more bleed (sound from one instrument leaking into another's microphone), the sound of everyone playing in one room at once. Vocals were captured as performances rather than as parts. Otis Redding cut the main vocal for "(Sittin' On) The Dock of the Bay" in December 1967, days before he died in a plane crash; the finishing touches — the famous waves and gulls — were added afterward by his studio partner Steve Cropper. It is the canonical Stax record.

Atlantic, the oldest of the three, ran its own soul operation through producers like Jerry Wexler. The company was based in New York, but it had its soul records made in the South — in Memphis and at Muscle Shoals, Alabama — where the players carried a rhythmic feel of their own. Aretha Franklin had been marketed as a jazz singer on Columbia through the mid-1960s without ever breaking through commercially; Wexler brought her to FAME Studios in Muscle Shoals in early 1967. The session collapsed in a single day after an argument involving her husband, and only one song was finished — but that song, "I Never Loved a Man (The Way I Love You)," remade her career completely.

While the soul labels were perfecting a song-form built on melody and chord changes, a parallel project was running in James Brown's band. The shift can be dated almost exactly to the summer of 1965 and the single "Papa's Got a Brand New Bag." The track is structurally still a soul song, but the rhythmic emphasis has moved. The downbeat is being hammered by the entire band rather than implied. The guitars are playing short, percussive figures rather than chords. The bass is locked to a repeating one-bar pattern rather than walking up and down a scale. You can hear Brown shouting his cues to the band on the record itself.

By the time of "Cold Sweat" (1967) and "Get Up (I Feel Like Being a) Sex Machine" (1970), the formula had hardened into what would later be called funk. The harmonic content was minimal — often a single chord for two or three minutes — and the rhythmic content was where the composition lived. Every musician played a small, repeating, locked pattern, and the patterns interlocked into a polyrhythmic whole — several rhythms running at once. A dancer could lock onto a different strand each time the loop came around. Brown's instruction to the band, captured on tape, was characteristic: "Everybody play on the one" — put every note on the first beat of the bar.

What funk really changed was the center of gravity of African-American popular music: it moved from the song to the groove. Few ran further with the idea than George Clinton's Parliament and Funkadelic, who stretched the locked groove across long, improvised jams and wrapped it in cosmic stagecraft and costumes. In doing so they became one of the central forces of what — after forerunners like the jazz bandleader Sun Ra, who had built a cosmic mythology decades earlier — would come to be called Afro-futurism: a Black vision of the future rendered in sound. Others took the same groove-first idea their own way: Sly and the Family Stone with mixed-race personnel and a psychedelic palette, and Earth, Wind & Fire — formed in Chicago and led by Maurice White — with the splendor of a full horn section layered over the groove.

Curtis Mayfield showed that funk could also carry social commentary. He used the new rhythmic vocabulary to score the 1972 film "Super Fly," and turned what was nominally a blaxploitation soundtrack — a movie made for Black audiences — into a clear-eyed album about drugs and poverty that reached number one on the US album chart and sold an estimated 1.5 million copies.

Funk on James Brown's records was built on syncopation. The kick drum hit on the first beat, the snare on beats two and four, and everything else organized itself around the asymmetry. Disco, which began to emerge in New York clubs in the early 1970s and was a fully named commercial genre by 1975, pushed the kick drum onto every quarter note — four even hits to the bar, on every beat. Four-on-the-floor.

The rhythmic flattening had a specific functional motivation. Disco's home was the DJ-driven dance club — the Loft, the Gallery, the Sanctuary, later Studio 54 and Paradise Garage — where a single DJ played a continuous evening's program by mixing one record into the next without stopping. Records with a steady, unmistakable kick were dramatically easier to beat-match than syncopated funk records. The four-on-the-floor pattern was a practical decision about how records would connect to each other on the night, before it was an aesthetic one.

The producers who built the genre understood this. Tom Moulton helped popularize the 12-inch single — cut with wider grooves, it ran louder and cleaner, and it became, as a result, the standard format for the long DJ mix. Giorgio Moroder, in Munich, built records around Donna Summer's voice — first the sultry, orchestral disco of "Love to Love You Baby" (1975), then "I Feel Love" (1977), where almost everything came from a Moog Modular synthesizer: a pulsing eighth-note bassline and most of the groove generated electronically, with only the kick supplied by a live drummer. The floor worked perfectly anyway, and "I Feel Love" made every subsequent electronic dance producer realize the pulse itself could come from a synthesizer alone. Chic, the group led by Nile Rodgers and Bernard Edwards — "Le Freak" (1978), "Good Times" (1979) — went the opposite way: no synthesizers, just live rhythm guitar and bass played with session-musician precision.

Months later, Sugarhill Gang's "Rapper's Delight" was built on the bassline of "Good Times" — that loping line of bass notes climbing and falling. A record made for dancing became the first record of an entirely new genre: the link between disco and hip-hop is a Chic bassline, the one Bernard Edwards played.

Stack the dates. "Papa's Got a Brand New Bag" arrives in 1965. By late 1967 "(Sittin' On) The Dock of the Bay" — soul at its peak — is recorded, and "Cold Sweat," which announces funk as a fully formed thing, lands in the same year. Sly's "Thank You" in 1969, "Get Up (I Feel Like Being a) Sex Machine" in 1970, "What's Going On" in 1971, "Super Fly" in 1972. Then the Hues Corporation's "Rock the Boat" — often cited as the first number-one disco single in the United States, though "Love's Theme" and "TSOP" have their advocates as earlier candidates — in 1974, "I Feel Love" in 1977, "Le Freak" in 1978. Ten years, three genres, connected in a continuous lineage.

The lineage is not metaphorical. Many musicians played in more than one of the three styles. Bernard Edwards started in soul session work before forming Chic. Marvin Gaye's later 1970s records ("Got to Give It Up," 1977) are functionally disco. At the Philadelphia International label, the producers Gamble and Huff, working with singers like the O'Jays and Harold Melvin, built a sound — Philly soul — that historians often file as proto-disco, the genre's immediate forerunner. The categories are useful shorthand, even if they oversimplify: the artists were never standing on opposite sides of a line.

What is more accurate is that over those ten years the dance floor itself was being engineered in real time. Soul gave the floor a song to sing along with. Funk gave it a polyrhythm, a different piece of it for everyone. Disco gave it a continuous, mixable kick pattern that the DJ could ride for six hours. The house records that young Chicagoans made on cheap drum machines in the 1980s are direct descendants of the four-on-the-floor those ten years settled on. The Afrobeats coming out of Lagos, Nigeria in the 2010s — the music Burna Boy and others carried around the world — belongs to the same family line, even if its core is not an even four-on-the-floor but a syncopated, percussive groove inherited from funk. The sequence Stax to James Brown to Donna Summer is the spine; everything since still dances on it.