Diatonic chord

Thirds on every degree

Start on any degree of a major scale and stack two thirds on it, skipping one scale note each time. That gives a triad made of notes from the scale. Repeat this on each of the seven degrees and you get seven chords that are guaranteed to fit together, because they all come from the same pool of notes. The quality of each chord follows from the intervals of the scale.

The order major–minor–minor–major–major–minor–diminished holds in every major key; only the note names change. Capital roman numerals mean major, lowercase minor, and the degree sign diminished.

Functions and substitutes

Three degrees carry the harmony: tonic (I), subdominant (IV) and dominant (V). The remaining degrees act as substitutes, because they share two notes with their main function. Degree vi (Am) stands in for the tonic, degree ii (Dm) for the subdominant. The move V–vi instead of V–I is the classic deceptive cadence. In minor the pattern changes: in natural minor the fifth degree is a minor chord (Em in A minor) because the scale lacks the leading tone, so the seventh degree is raised and this gives harmonic minor. The full derivation is on the page Diatonic chords.

The same in every key

Roman numerals are a key-independent shorthand. I–V–vi–IV means C–G–Am–F in C major and G–D–Em–C in G major: same function, same effect. If you think in degrees, you transpose effortlessly and recognise patterns.

Common mistakes

• Taking the second degree for major: On the second degree there is a minor third at the bottom, which gives minor.
• Overlooking the degree sign: vii° is diminished, not minor.
• Learning degrees only for major: In minor the order of the qualities changes.