Building triads from intervals

You have played chords for a long time without needing to know why they are what they are. This lesson shows how a triad is built from a root, a third and a fifth, and why changing one note turns major into minor.

By the end of this lesson you will be able to:

• State the formulas for major (1 3 5) and minor (1 ♭3 5) triads.
• Spell major and minor triads from any natural root.
• Name the notes in an open chord shape and spot the doubled notes.

A triad is three notes stacked in thirds: a root, a third above it and a fifth above that.

• Major triad: root, major third (4 semitones), perfect fifth (7). Formula 1 3 5.
• Minor triad: root, minor third (3 semitones), perfect fifth (7). Formula 1 ♭3 5.

The only difference between major and minor is the third, one fret. The fifth is the same in both.

Spelling a triad. Use the major scale. For G major (G A B C D E F♯), take the 1st, 3rd and 5th notes: G B D. For the minor, lower the third by a semitone: G B♭ D.

Examples with the notes written out:

• A major: A C♯ E. A minor: A C E.
• D major: D F♯ A. D minor: D F A.
• E major: E G♯ B. E minor: E G B.
• C major: C E G. C minor: C E♭ G.

Every chord shape contains only three note names, repeated across the strings. An open A minor played as x02210 gives A, E, A, C, E: only A, C and E.

Finding the third. Play E major (022100) and pick each string from the low E: E, B, E, G♯, B, E. The G♯ is the only note that is neither E nor B. That is the third.

Now lift the finger from the G string. The open G is a semitone lower: G. You are playing E minor (022000).

Do the same with A. Play A major (x02220) and find the note on the B string, fret 2: C♯, the third. Lower it by one fret, to fret 1, and the chord becomes A minor (x02210, with the first finger on the B string and the others on the D and G strings). The only change that matters is the third.

Hear the difference. Major and minor triads differ by one note, and you can hear it. Name each triad you are played.

Do these in order. Each one is small. Tick the ones you have practised.

• 1.Spell it

  4 min

  1. Write out the major scale from A, D, E and G.
  2. For each, take the 1st, 3rd and 5th notes: that is the major triad.
  3. Lower the 3rd by a semitone to get the minor triad.
  4. Check against the open chord shapes.

  You have it when

  • You get A C♯ E, D F♯ A, E G♯ B and G B D for the majors, and the correct minors.
  I practised this one

• 2.Find the notes in a shape

  4 min

  1. Play open Am (x02210) one string at a time and name each note: A, E, A, C, E.
  2. Notice that only three note names appear: A, C, E. The others are repeats.
  3. Do the same with Em (022000) and C (x32010).

  You have it when

  • You can name every note in Am, Em and C and say which are repeated.
  I practised this one

• 3.Flatten the third

  4 min

  1. Play E major (022100). The third, G♯, is on the G string (fret 1).
  2. Lift that finger. The open G string is a G, one semitone lower: you now have E minor.
  3. Do the same from A major: lower the C♯ on the B string (fret 2 to fret 1) to get A minor.

  You have it when

  • You can turn E into Em and A into Am by changing just the third, and explain why.
  I practised this one

This is a thinking lesson with some playing. No tempo is needed. If you use a metronome, 50 BPM with four beats per chord is plenty.

• Learning chords as shapes only. Every shape is just three note names repeated. Know the names and you can build the chord anywhere.
• Mixing up the order of major and minor thirds. A major triad is a major third then a minor third (4 + 3 semitones). A minor triad is the reverse (3 + 4).
• Using the wrong letter when spelling. A triad skips a letter each time: C E G, D F♯ A. Use the right sharps or flats to get the right distance.

Every chord progression you play is made of triads. Knowing how they are built lets you work out unfamiliar chords, change them to minor or major on purpose, and understand how they relate to each other.

Try it in: Let It Be.

Short version (10 minutes)

Spell the major and minor triads for A, D, E and G out loud, then check them on the guitar.

Standard version (about 30 minutes)

Do all three exercises, then pick two songs from the library and write the notes of each chord.

• A triad is a root, a third and a fifth.
• Major: 1 3 5. Minor: 1 ♭3 5.
• Lowering the third by one fret turns major into minor.
• Any chord shape contains only three note names.

You are ready to move on when you can honestly say:

• I can state the major and minor triad formulas.
• I can spell the major and minor triad on any natural root.
• I can name the notes in an open chord shape.