A chord is more than one note sounding together. But not just any pile of notes — chords are built by a simple rule: stack notes a third apart. Start on a note, skip one, take the next; skip one, take the next. Three notes stacked this way is the smallest complete chord — a triad.
Stacking in thirds
Take C, skip D, land on E. Skip F, land on G. Those three notes — C, E, G — are a C major triad.
Why thirds, and not seconds or fourths? A second (C–D) is so close it sounds muddy; a fourth or more is so wide it stops feeling like one unit. A third is the sweet spot where notes blend into a single, stable colour — so Western harmony makes the third its building block.
Chord tones
The notes that make up a chord are its chord tones. A triad has exactly three, and each has a name and a job:
| Chord tone | Degree | Job |
|---|---|---|
| Root | 1 | Names the chord — a chord with C on the bottom is some kind of C. |
| Third | 3 | Sets the mood — a big third sounds major, a small one minor. |
| Fifth | 5 | Adds stability — shrink or stretch it and the chord turns tense (dim / aug). |
The four triad qualities
Change the size of the thirds you stack and you get four different flavours from the same three scale degrees:
| Quality | Notes | How it's stacked |
|---|---|---|
| Major | C · E · G | major 3rd + minor 3rd |
| Minor | C · E♭ · G | minor 3rd + major 3rd |
| Diminished | C · E♭ · G♭ | minor 3rd + minor 3rd |
| Augmented | C · E · G♯ | major 3rd + major 3rd |
That's it — every basic chord is two stacked thirds, and which two decides the quality.
Keep stacking: 7ths, 9ths and beyond
Nothing says you have to stop at three. Keep skipping-and-stacking and the chord gets richer:
- The triad (1·3·5) is the core.
- Add the 7th and you get a seventh chord — smoother, more sophisticated.
- 9, 11, 13 are tensions: colour notes you add on top for extra flavour.
Chord tone or passing note?
Here's a point that trips people up. During a stretch of C major, do you only ever hear C, E and G? No — other notes show up too. The same note can play two completely different roles:
Passing note. A melody moving C → D → E just brushes past the D on its way. The chord is still C; the D belongs to the melody, not the chord. It's a non-chord tone.
Added tension. Hold that same D down inside the chord and it joins the harmony as the 9th — now you have Cadd9 (C·E·G + D).
Same D, two jobs: brush past it and it's a passing note; press it into the chord and it's a chord tone. Whether a note "belongs" is about how it's used, not the note itself.
See it on the neck
Here's the I chord of C major as a triad on the top three strings, shown in all three inversions at once — the same three notes, reachable in three shapes up the neck:
In one line: a chord is notes stacked in thirds — the basic triad is 1·3·5. Stack higher (7·9·11·13) for richer colour, and remember that a note like D over a C chord is a passing note when you brush past it, a tension when you hold it in.