Three chords, twelve bars, and almost the whole family tree of American music grows out of it — blues into rock into soul into hip-hop. Tap PLAY to walk the form, slide the tempo, swing it, and hear the ancestor the whole canon descends from.
The twelve-bar blues: a fixed 12-bar form over three chords — I, IV, V — here the standard quick-change pattern (I·IV·I·I / IV·IV·I·I / V·IV·I·V). Tap PLAY and the page walks the bars in tempo, sounding each chord as a live dominant-7th (root·3·5·♭7 — the bluesy chord) through Web Audio; the bar counter and current chord track along. Shuffle applies the triplet swing feel. All generated from the roman-numeral form — real, playable music history, no recording.
A single canonical 12-bar pattern with block dominant-7ths stands in for a living tradition of turnarounds, substitutions, riffs and feel that no grid captures; 'the whole canon descends from it' is a claim about influence, not a strict genealogy. The form, the I–IV–V voicings and the tempo are exact and played live.