The blues is a chair, not a design for a chair or a better chair . . . it is the first chair. It is a chair for sitting on, not for looking at. You sit on that music.
Lennon meant that the blues is the template, that all music that follows is other people's attempts to create the blues. Every song is another chair in the auditorium.
Elvis wasn't trying to create a whole new genre of music, he was just doing a cover of a blues song, That's all Right, Mama, but being a white boy with a country band it sounded new and different. The Beatles weren't trying to drag music out of the 50s into the 60s - they were trying to be Elvis. But they were Scouse and rowdy and their chairs sounded different too. And when the Clash rejected Elvis, Beatles and Rolling Stones in 1977 they did it with two guitars, bass and drums. The Clash, the Pistols, Led Zep, Radiohead, the Beach Boys, the Byrds, Robin Thicke, they were all just trying to create a new blue chair.
Blue Chair, Elvis Costello