The major scale is the “source code” and diatonic 3rds are one of the quickest ways to see how triads, sevenths, arpeggios and modes are all derived. Here’s C major in diatonic thirds (everything comes straight from the scale — no sharps/flats). Up top is the Circle of Thirds showing the quality of each 3rd: 🟩 Major 3rd = two whole steps 🟧 Minor 3rd = W–H (or H–W) inside the scale Practice ideas: • Run it up and down • Switch string pairs (watch the G → B jump 👀) • Move it to a new root note