Triads and Chords

When you play a single note you hear a pitch. When you play several notes together you hear a chord. A chord is three or more notes sounding at the same time, and it is the basic building block of harmony. This lesson introduces the most common chord of all: the triad.

Stacking thirds

A triad is built by stacking intervals of a third. Start on a note, skip one letter, land on the next, then skip again. That gives you three notes: the root (the note the chord is named after), the third above it, and the fifth above the root. On C, that is C, E and G.

What makes a chord sound bright or dark is not the letters but the exact size of those intervals, measured in semitones (the distance from one key to the very next key). The third decides whether a triad is major or minor, and the fifth adds colour on top.

The four triad qualities

• Major: a major 3rd (4 semitones) plus a perfect 5th (7 semitones). Bright and stable.
• Minor: a minor 3rd (3 semitones) plus a perfect 5th (7). Darker and softer.
• Diminished: a minor 3rd (3) plus a diminished 5th (6). Tense and unsettled.
• Augmented: a major 3rd (4) plus an augmented 5th (8). Strange and suspended.

Here are all four qualities built on the root C so you can compare them directly:

Notice how small the changes are. Lowering just the third turns C major into C minor. Lower the fifth as well and you reach C diminished. Raise the fifth of a major triad instead and you get C augmented. One shifted note completely changes the mood.

Beyond three notes

Triads are only the start. If you keep stacking thirds you add a fourth note a 7th above the root, which creates a seventh chord. C major plus a B gives a rich C major 7th; C major plus a B♭ gives the restless dominant C7 that pulls strongly toward the next chord. Seventh chords add warmth, tension and colour that plain triads cannot.

The best way to hear these differences is to build the chords yourself. Use the explorer below to pick a root, switch between major, minor, diminished and augmented, and listen for how the third and fifth reshape each chord.

Every chord you will ever meet grows from this idea: stack notes in thirds, then adjust the third and fifth. Master the four triads and the whole language of harmony opens up.