Why are 2nds, 3rds, 6ths, and 7ths major or minor, but 4ths, and 5ths are diminished, augmented, or perfect? I might have some of that a little mixed up and I realize some are enharmonic equivalents.

This is, I suppose, more an etymological question than a pure music theory but I thought this might be the right place to ask.

  • I wasn't sure if the linked duplicate did fully answer my question but the point about a fifth being an inverted fourth really made it click for me. Thank you to those who linked me to what I had trouble finding. – user3140009 Sep 18 '19 at 17:09

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