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Chords & Harmony

Primary Chords (I, IV, V)

Definition

The primary chords are the triads built on degrees 1, 4 and 5 of a scale: I, IV and V. In C major they are C, F and G. Together they contain every note of the scale, so they can harmonize most simple melodies.

The primary chords are the three triads built on the first, fourth and fifth degrees of a scale: the tonic chord (I), the subdominant chord (IV) and the dominant chord (V). In C major they are C, F and G; in G major, G, C and D. In a major key all three are major chords, which is why they are written with capital Roman numerals.

Why these three?

Between them, the three primary chords contain every note of the scale: C–E–G, F–A–C and G–B–D cover all seven notes of C major. So almost any note of a simple melody belongs to at least one of them. They also stand for the three harmonic functions: home (I), moving away (IV) and pulling back home (V). That is why so many folk songs, hymns, country songs and early rock and roll songs need only these three chords, and why guitarists call them the "three-chord trick".

Playing them in the closest positions

Beginning pianists usually learn the primary chords in shapes that keep the left hand in one place: C–E–G for I, C–F–A for IV (in second inversion) and B–F–G for V7 (in first inversion, without its fifth). Each change moves only one or two fingers, by a step.

Two bass-staff panels in 4/4, three bars each. C major: half-note chords C3 E3 G3, C3 F3 A3, C3 E3 G3, B2 F3 G3, then a whole-note C3 E3 G3, labeled C, F/C, C, G7/B, C and I, IV6/4, I, V6/5, I. A minor: A2 C3 E3, A2 D3 F3, A2 C3 E3, G-sharp2 B2 E3, then A2 C3 E3, labeled Am, Dm/A, Am, E/G-sharp, Am and i, iv6/4, i, V6, i.
Top: I – IV – I – V7 – I in C major, using the shapes C–E–G, C–F–A and B–F–G. Bottom: i – iv – i – V – i in A minor, using A–C–E, A–D–F and G♯–B–E.

Primary chords in a minor key

In a minor key the tonic and subdominant chords are minor (i and iv), while the dominant is usually major (V), thanks to the raised seventh degree of the harmonic minor scale. In A minor they are Am, Dm and E.

Harmonizing a melody with I, IV and V

  1. Look at the melody notes on the strong beats of each bar.
  2. Find the primary chord that contains them. In C major, E points to I, A to IV, and B and D to V. C and G each belong to two chords (C to I and IV, G to I and V), so let the other notes in the bar decide.
  3. End phrases with V–I for a full close, or stop on V for a pause (see cadence).

Harmonize a melody walks you through it, and The Primary Chords in Every Key lists them in all 24 keys.

Common questions

What are the primary chords in G major?

G major (I), C major (IV) and D major (V). Add a seventh to the last one and it becomes D7 (V7).

What are the primary chords in a minor key?

i, iv and V. In A minor they are A minor, D minor and E major; the E chord is major because the seventh degree, G, is raised to G♯.

Practice it: free worksheets