Music

In the Renaissance the third and the sixth stop being second-class intervals and become primary consonances. Here's the sweet English sound and fauxbourdon, pervading imitation, the three stages of mass technique, and the opposite directions Palestrina and Gesualdo took at the end — with sheet-music examples you can play right in the page.

Medieval music treated the perfect unison, fifth, and octave as sacred and the third as imperfect. Here’s the background — the idea that simple whole-number ratios mirror divine order — plus modes, organum, and cadences, each with sheet-music examples you can play right in the page.