How Triads Are Built: Major, Minor, Diminished and Augmented Chords

A triad is a three-note chord built by stacking two thirds on top of a root. Triads are the foundation of tonal harmony, and nearly every chord you hear in pop, folk and classical music is a triad or a triad with extra notes added. This guide shows how the four triad qualities are constructed, how their semitone patterns differ, and how to spell them correctly from any root.

Stacking thirds

A triad has three parts: the root, the third above the root, and the fifth above the root. The third and fifth are both built by counting letter names, so a third is a step of two letter names and a fifth is a step of four letter names. The root gives the chord its name, while the quality depends on the size of the third and fifth.

Because triads stack thirds, they are sometimes called tertian chords. Adding another third above the fifth creates a seventh chord, which is covered in a separate guide.

The four triad qualities

Triads come in four qualities. Each quality is defined by the number of semitones between the root and the third, and between the third and the fifth. The table below summarizes the four types.

Quality	Root to third	Third to fifth	Total semitones	Symbol
Major	4	3	7	C, C maj
Minor	3	4	7	Cm, C min
Diminished	3	3	6	C dim, C°
Augmented	4	4	8	C aug, C+

Major and minor triads share the same total span of seven semitones, the perfect fifth, and differ only in where the third sits. Diminished and augmented triads alter the fifth, lowering it or raising it by one semitone.

The major triad

A major triad has a major third and a perfect fifth above the root. In C, the notes are C, E and G. The bright sound of the major triad comes from the major third, which matches the simple five-to-four frequency ratio in just tuning. Major triads sound stable and open, which is why they often mark the beginning or end of a phrase.

To spell a major triad from any root, use the root, the note four semitones above it, and the note seven semitones above it. For F, that gives F, A and C.

The minor triad

A minor triad has a minor third and a perfect fifth above the root. In C minor, the notes are C, E flat and G. The only change from the major triad is that the third is lowered by one semitone, and this single change produces the darker, more inward sound that listeners associate with minor keys.

To spell a minor triad from any root, use the root, the note three semitones above it, and the note seven semitones above it. For A, that gives A, C and E.

The diminished triad

A diminished triad has a minor third and a diminished fifth above the root. In B, the notes are B, D and F, which spell the diminished fifth as F, six semitones above B. The diminished triad is tense and unstable, and it usually wants to resolve to a stable chord that contains its notes.

Diminished chords are common in classical harmony and in jazz, where they form the basis of the diminished seventh chord. They appear in many song progressions as passing chords.

The augmented triad

An augmented triad has a major third and an augmented fifth above the root. In C, the notes are C, E and G sharp. The augmented fifth is eight semitones above the root, which means the three notes divide the octave into equal major thirds. Because of this symmetry, an augmented triad has no clear sense of a home key, and composers use it for color and ambiguity.

Augmented triads often appear as dominant-like sounds in romantic harmony and in film and jazz writing.

Spelling triads correctly

Spelling is the difference between a chord you can read and a chord that looks wrong on the page. Each triad needs one note from each letter name in the sequence root, third and fifth, so a chord named C major must use C, E and G, not C, F flat and G. For a diminished triad on B, the fifth must be F rather than G flat, because G flat sounds as F sharp, a perfect fifth above B.

The rule is simple. Write the three letter names in order, then add or lower accidentals until the semitone counts match the quality in the table.

Triads built on the notes of a major scale follow a fixed pattern. Degrees one, four and five form major triads, degrees two, three and six form minor triads, and degree seven forms a diminished triad. Checking a chord against the scale is often faster than memorizing each spelling, and it shows why certain chords feel close to home in a key while others feel distant.

Inversions

A triad can be arranged with a note other than the root at the bottom. When the third is in the bass, the chord is in first inversion. When the fifth is in the bass, it is in second inversion. The notes stay the same, but the bass note changes the chord's function and sound. Composers use inversions to create smooth bass lines and to avoid large jumps between chords.

Classical analysis labels inversions with figured bass numbers. Root position is written 5/3, meaning the fifth and third sit above the bass. First inversion is written 6/3, and second inversion is written 6/4. These numbers tell you the intervals above the bass, so a student can read a bass line and infer the chord before seeing the upper notes.

Practice routine

Build each triad quality on familiar roots first. Use C major, C minor, B diminished and C augmented, then repeat each one on F, G and A. Play the root, then count semitones up to the third and fifth. Finally, name the chord from the notes you played, not from memory, so that spelling and sound stay connected.

Sing the third and fifth of each chord after you play it. Hearing the major third and minor third against the same root is the fastest way to learn the difference between major and minor.

Key takeaways

A triad is built from a root, a third and a fifth. The third and fifth sizes determine whether the chord is major, minor, diminished or augmented.

Major and minor triads use a perfect fifth, while diminished and augmented triads alter the fifth. Each quality has a distinct semitone pattern that you can count on any keyboard.

Practice spelling triads by letter name first, then check the semitone counts. With that routine, you can build any triad from any root and understand what each one contributes to harmony.