Chords and harmony: triads and primary chords

A chord is several notes played at the same time. Chords give a melody its harmony, like the background colour behind a picture.

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Building a triad

A triad is a three-note chord made of a root, a third and a fifth.
On a keyboard: play a note, skip a note, play a note, skip a note, play a note. Starting on C gives C E G: a C major chord.
The root is the note the chord is named after.
A major chord sounds bright; a minor chord, such as A C E (A minor), sounds darker.

Primary chords

In any major key, the three primary chords are built on the 1st, 4th and 5th notes of the scale. They are labelled with Roman numerals: I, IV and V.
Chords I, IV and V together contain every note of the major scale, so they can harmonise many simple melodies.
KeyIIVV
C majorC (C E G)F (F A C)G (G B D)
G majorG (G B D)C (C E G)D (D F# A)
F majorF (F A C)B flat (B flat D F)C (C E G)

Using chords

A chord sequence (or chord progression) is a series of chords. For example: C, F, G, C (I, IV, V, I).
To choose a chord for a melody note, pick a chord that contains that note. For the note E in C major, chord I (C E G) fits.
Chords can be played as block chords (all notes together) or as broken chords (one note at a time).
Consonant chords sound stable and restful; dissonant combinations sound clashing and tense.
Worked example

A melody in C major has the note A. Which primary chord contains it?

  1. The primary chords in C major are C (C E G), F (F A C) and G (G B D).
  2. Look for A in each chord.
  3. Only F (F A C) contains A, so use chord IV.

Answer: Chord IV, F major (F A C).

Key idea

A triad is a root, third and fifth. The primary chords are I, IV and V: in C major, C, F and G. Choose a chord that contains the melody note. Consonance sounds stable; dissonance sounds tense.

Key words
Chord
Two or more notes played at the same time.
Triad
A three-note chord: root, third and fifth.
Dissonance
Notes that clash and sound tense.
Sequence
A motif repeated starting on a higher or lower note.

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Extra practice

2 more questions

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  1. Which notes make a G major triad?

    1. G B D
    2. G A B
    3. G C E
    4. G B F
    Show the answer

    Answer: G B D

    Root G, third B, fifth D.

  2. In G major, which are the three primary chords?

    1. G, A and B
    2. G, C and D
    3. G, B and D
    4. C, F and G
    Show the answer

    Answer: G, C and D

    I, IV and V in G are G, C and D.

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Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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