Triad Chords
Senior 3 · Music
Triad Chords
Lesson 4 of 4
30 min
A guitarist who knows only three chords in a key can already accompany many simple songs: hymns, school songs, children's songs and much popular music. Those three are the triads on the first, fourth and fifth degrees of the scale. They are called the primary chords, and in this lesson you use them to harmonise a melody and to end a phrase with a cadence.
Definition
Primary chords: the triads on the tonic (I), subdominant (IV) and dominant (V) of a key. In a major key all three are major. In a minor key (harmonic) they are i (minor), iv (minor) and V (major). Example in C major: C–E–G, F–A–C and G–B–D.
Secondary chords: the other diatonic triads, ii, iii, vi and vii° in a major key.
Cadence: the two chords that close a musical phrase, like punctuation at the end of a sentence.
Look at the notes of I, IV and V in C major. Between them they contain every note of the scale, so whatever note the melody sings, at least one primary chord fits it.
| Key | I (tonic) | IV (subdominant) | V (dominant) |
|---|---|---|---|
| C major | C–E–G (C) | F–A–C (F) | G–B–D (G) |
| G major | G–B–D (G) | C–E–G (C) | D–F♯–A (D) |
| F major | F–A–C (F) | B♭–D–F (B♭) | C–E–G (C) |
| D major | D–F♯–A (D) | G–B–D (G) | A–C♯–E (A) |
| A minor (harmonic) | A–C–E (Am), i | D–F–A (Dm), iv | E–G♯–B (E), V |
In tonic sol-fa the primary chords of any major key are always d–m–s (I), f–l–d' (IV) and s–t–r' (V), which is why a choir trained in sol-fa can sing them in any key.
To choose a chord for each bar: (1) list the main notes of the bar, especially those on strong beats; (2) find the primary chord that contains them; (3) begin and end on I, and put V just before the last I. Here is a short melody harmonised that way:
Worked example
Worked example 1: choose the chord. A bar of a song in G major has the notes D, F♯ and A on its strong beats. Which primary chord fits?
Worked example
Worked example 2: name the cadence. A phrase in F major ends with the chords C–E–G then F–A–C.
On a keyboard. Play the chords C, F, G and C (I–IV–V–I) with the left hand, one chord per bar, four beats each, while a classmate sings or plays the melody above. To move smoothly, keep any note the two chords share: from C–E–G to F–A–C, play the F chord as C–F–A so that C stays under the same finger.
With voices. Split the class into three groups. On each chord, group 1 sings the root, group 2 the third and group 3 the fifth, in sol-fa: d–m–s, then f–l–d', then s–t–r', then d–m–s. Finish with the plagal cadence f–l–d' to d–m–s on "A-men".
Video: "Primary Chords", MusicTheoryAcademy. How to work out chords I, IV and V in any key and use them to write music. Pause when a new key appears and write its three chords before the presenter shows them.
Tip
Shared notes. I and IV share the tonic; I and V share the dominant. When a melody note belongs to two chords, choose the one that also fits the other notes of the bar.
Warning
Common mistake: using the minor v in a minor key, or forgetting the key signature in V. In A minor the dominant is E–G♯–B, and in D major it is A–C♯–E. Without the sharp, the perfect cadence loses its pull.
Practice
Remember
Further reading
Sources and credits
