Sam Parkins, wily explorer of the reeds, is also a phenomenal writer. Here’s a snippet from his memoirs about Louis’s approach to the harmonic “modernism” that so shaped the jazz of the times:
I heard Louis Armstrong the music critic at that dance in Lexington KY, spring 1945. A very clear statement about his loathing for modern music, coming at him like a tornado. Music lesson: For preceding centuries, a song or a complete chorus ended on what’s called the “tonic” – the home key, and the chord that preceded it was called the “dominant”, 4 notes below. Here comes modern, and by 1944 the “dominant” was often replaced by a somewhat purple 7th chord a half-step above the “tonic”. Let’s put our mythical tune in the key of F major; at least 20% of the standard repertoire is in F. Eddie Condon called F “the key of love”. Means the traditional “dominant” chord is C, usually with a 7th. So I’m grooving away with Louis blowing his heart out over the band, and come to an ending, where his up-to-date arranger has modernized things with a G-flat 7th before the “tonic” F. Louis slashes an angry C triad right across it, making him play at least two “wrong” notes, and Louis was incapable of playing wrong notes. “That for your godamned modernism!”.