Chords
The chords that live inside each key, organized by scale degree. Each row is a key (ordered by the circle of fifths, so adjacent rows differ by only one chord) and each column is a function within the key. Below the basic triad charts you'll find a few common extensions: seventh chords, suspensions, and slash chords (first- and second-inversion triads).
Diatonic triads — major keys
The seven triads of every major key: I, ii, iii, IV, V, vi, vii°. The I, IV, and V are major; the ii, iii, and vi are minor; the vii° is diminished. These sixchord-quality patterns are constant across all twelve major keys.
Diatonic triads — minor keys
The seven triads of every natural minor key: i, ii°, III, iv, v, VI, VII. Minor keys are darker because the i chord is minor and the dominant (v) is also minor rather than major.
Diatonic seventh chords
Add a 7th to each triad and the chord palette becomes richer: every triad grows a fourth note that sits a 3rd above its 5th. The qualities for a major key are Imaj7, ii7, iii7, IVmaj7, V7, vi7, vii⌀7 (half-diminished). These are the bedrock of jazz, soul, and any style with more harmonic color than three-note triads provide. The V7 in particular has a strong pull back to the I and is the engine of most chord progressions in tonal music.
Suspended chords
A sus chord replaces the 3rd of a triad with either a 2 (sus2) or a 4 (sus4). With no 3rd, the chord sounds neither major nor minor — tonally suspended, hence the name. Most often you'll see sus chords built on the I, IV, and V of a major key; the others can clash with the diatonic scale. Sus chords most often resolve back to the regular triad they came from (Csus4 → C), which gives a satisfying release of tension. Common in folk, pop, and almost every genre that uses acoustic guitar.