Triads: from the root to the chord’s three notes

What exactly is a triad?

A triad is a chord class containing three different pitch classes that can be arranged as stacked thirds. In ordinary major/minor harmony, these are the root (1), third (3) and fifth (5). A triad has three distinct chord tones even if the guitar plays six strings or the piano doubles notes in several octaves.

Take C–E–G. C is the root, E the third and G the fifth. C to E is four semitones, a major third; E to G is three, a minor third. C to G is seven, a perfect fifth.

Building triads by taking alternate scale notes helps find chords within a key. Remember that scale degrees determine the note letters selected, while intervals determine the resulting chord quality.

Four triad types: what changes?

Keep C as root and change only the third or fifth. This makes each note’s contribution easier to hear.

Major and minor have a perfect fifth and differ in the third. A diminished triad has a minor third and diminished fifth, six semitones above the root. An augmented triad has a major third and augmented fifth, eight semitones above the root.

Find the triads in C major

Use what you know from building chords in a key. Start with C–D–E–F–G–A–B and take alternate notes. This gives seven diatonic triads: three major, three minor and one diminished.

Not every chord in the key of C major is a C-major chord. They share a key, but the intervals within each triad differ. Moving the system to G major keeps I–ii–iii–IV–V–vi–vii°, while the chord names change.

Root position and inversions: same chord, new bass

The notes of C major are C, E and G. C–E–G with C lowest is root position. With E lowest, arrange them as E–G–C: first inversion, commonly C/E. With G lowest, G–C–E is second inversion, commonly C/G.

The chord’s root remains C in all three. The root is not necessarily the lowest note. Inversions can make bass lines smoother and shorten voice movements without changing chord identity.

In Roman-numeral analysis, I6 usually means first inversion and I6/4 second inversion. This does not automatically mean a C6 chord with added A. The 6/4 figures refer to intervals above the bass in figured-bass practice.

Move one note and hear the change

Spend time on this exercise. Play C–E–G slowly. Keep C and G while lowering E to E♭: C major → C minor. Keep C and E♭ and lower G to G♭ for Cdim. Return to C major and raise G to G♯ for Caug.

On piano, hold two notes and move the third. On guitar, first play individual notes on one or more strings, then find a shape containing the same three pitch classes. The finger pattern is not the explanation; you are investigating the intervals.

Describe what you actually hear. Major is not always happy, nor minor always sad. Timbre, register, tempo and context affect the result. Aim to recognise which note changed rather than memorising a fixed emotional description.

From triads to seventh chords

Once you understand triads, add one more chord tone by continuing the stack of thirds. Add B to C–E–G for Cmaj7: C–E–G–B. B is a major seventh above C.

Add B♭ instead for C7: C–E–G–B♭, a dominant-seventh chord type. C7 need not be the actual dominant of the key; the name primarily describes its construction.

Add B♭ to C–E♭–G for Cm7: C–E♭–G–B♭. Root, third and fifth remain the foundation. That is why we learn triads first.

Next: seventh chords, more colour on the same foundation ↗

The method: hear, predict, play, explain, change

Hear: Play C major, C minor and Cdim as arpeggios. Predict: Sing the note that must move to turn C major into minor. Play: Check on the instrument and try all three inversions of C major. Explain: Identify root, third, fifth and bass in C/E. Change: Write a progression using an inversion to give the bass stepwise motion.

For example: C → G/B → Am. The bass becomes C–B–A. G/B contains G–B–D with B in the bass. You have used an inversion to create musical movement, rather than merely learning a shape.

Move from knowing which notes form a chord to understanding how those notes can approach the next chord. That makes maj7, m7 and dominant-seventh chords easier to learn.