Diatonic chords

Build a triad on EVERY degree of a scale, using only the scale's own notes, and you get the seven DIATONIC CHORDS of that key — the chords its songs are made of.

They are written as Roman numerals: uppercase = major, lowercase = minor, ° = diminished. In every major key: I, ii, iii, IV, V, vi, vii°. In C major: C, Dm, Em, F, G, Am, B°.

This is why chord progressions are portable: I–V–vi–IV is the same song in any key. In minor keys the pattern is: i, ii°, III, iv, v, VI, VII.

To play "the IV chord of C major": find the 4th degree (F), then stack two scale thirds on it: F–A–C.

major keys: I · ii · iii · IV · V · vi · vii°

The IV chord of C major: F–A–C, built on the 4th degree.

Practise this in the trainer — it opens with this lesson the first time the concept comes up.