A triad is a three-note chord built in thirds: a root, the note a third above it, and the note a fifth above it. C–E–G is a C major triad. Changing the third and fifth by a semitone gives the four kinds of triad: major, minor, augmented and diminished.
By Dan Vrancic, music theory teacher · Reviewed October 2026
What is a triad?
A triad is three notes stacked in thirds: every other letter name. The bottom note is the root, which names the chord; above it are the 3rd and the 5th. Written in root position, the three notes sit on three lines in a row or three spaces in a row.
On lines
C–E–G
On spaces
F–A–C
The notes can sound together (a solid or blocked chord) or one after another (a broken chord or arpeggio). Either way, it is the same triad.
The four types of triad
Every triad has one of four qualities. Start from the major triad, the 1st, 3rd and 5th notes of the root's major scale, and move the 3rd or 5th by a semitone:
Triad
Formula
3rd
5th
Semitones
Symbol
Major
1 · 3 · 5
Major 3rd
Perfect 5th
4 + 3
C
Minor
1 · ♭3 · 5
Minor 3rd
Perfect 5th
3 + 4
Cm
Augmented
1 · 3 · ♯5
Major 3rd
Augmented 5th
4 + 4
C+
Diminished
1 · ♭3 · ♭5
Minor 3rd
Diminished 5th
3 + 3
C°
One root, four qualities. Only the 3rd and the 5th move.
Major triads sound bright and stable, minor triads darker. Diminished triads sound tense, and augmented triads sound unresolved, as if they need to move on.
How to identify a triad
Find the root
Stack the notes in thirds. The bottom note of the stack is the root.
Think in the root's major key
Name the 3rd and 5th of the root's major scale.
Compare the 3rd and 5th
Same notes: major. 3rd a semitone lower: minor. Both lower: diminished. 5th a semitone higher: augmented.
F♯ major has A♯ and C♯. Here A and C are each a semitone lower, so F♯–A–C is F♯ diminished.
Triads in a key
Build a triad on each note of a scale, using only the notes of the key, and you get the key's seven diatonic triads. They are numbered with Roman numerals: upper case for major, lower case for minor, ° for diminished and + for augmented.
The seven triads of C major.
The pattern is the same in every major key: I ii iii IV V vi vii°. The triads on degrees 1, 4 and 5, I, IV and V, are the primary triads: tonic, subdominant and dominant.
In a natural minor key the pattern is i ii° III iv v VI VII. Harmonic minor raises the 7th, which makes the dominant a major V and the triad on 7 a diminished vii°, the chords that give minor-key cadences their pull.
The seven triads of A natural minor.
Try it: name the triad
Triad 1 of 6
D–F–A: what kind of triad is it?
See it step by step
The interactive explainer from Lesson 18, with sound. Step through it at your own pace.
See it take shape · Interactive story
One root, four qualities
Stack two 3rds above a root and you have a triad. Hold the root still and move one note by a semitone: the letters stay, and the chord becomes major, minor, augmented or diminished.
Step 1 of 11
Start on C and skip a letter…
Skip a letter
A triad is a stack of 3rds
Start on C, skip D, take E; skip F, take G. The bottom note is the root, the middle note is the 3rd and the top note is the 5th, each named by its distance from the root.
Root, 3rd, 5th: skip a letter each time.
Use the arrow keys while a story control is focused.
Read the story as text
A triad is a stack of 3rds
Start on C, skip D, take E; skip F, take G. The bottom note is the root, the middle note is the 3rd and the top note is the 5th, each named by its distance from the root.
Three lines or three spaces
Because each note skips a letter, a triad in root position sits on three lines in a row or in three spaces in a row. C–E–G uses lines; F–A–C uses spaces.
Solid or broken, it is the same triad
Written one above the other, the notes sound together: a solid (blocked) triad. Spread out, they sound one after the other: a broken triad. The notes, and the name, do not change.
Major: 1, 3 and 5 of the root’s major key
Think in the major key of the root and take its 1st, 3rd and 5th notes. C to E is a Major 3rd and C to G is a Perfect 5th: a Major triad. Try F, G and D: D major’s 3rd is F♯, so D Major is D–F♯–A.
Minor: lower the 3rd
Keep C and G and lower E to E♭. The note stays on its line, so it is still a 3rd, but now a minor 3rd. The 5th is still Perfect, and the triad is C minor.
Major ↔ minor: change one accidental
To rewrite a triad, find its 3rd and move it a semitone, keeping the letter. D–F♯–A becomes D–F–A; A–C–E becomes A–C♯–E. The root and 5th never move.
Augmented: raise the 5th
Start from C Major and raise the 5th from G to G♯. The 3rd stays Major and the 5th grows from Perfect to Augmented: C augmented, written C+.
Diminished: lower the 5th
Start from C minor and lower the 5th from G to G♭. The 3rd stays minor and the 5th shrinks from Perfect to diminished: C diminished, written C°. Both notes above the root are now lowered.
Every root has all four
Choose a root and a quality. The 3rd and 5th always come from the root’s major key first, then move: lower the 3rd for minor, raise the 5th for augmented, lower both for diminished.
Name a triad in three moves
Find the root: the bottom note when the triad is stacked in 3rds. Think in its major key to find the Major 3rd and Perfect 5th. Then compare the written 3rd and 5th with them and read the quality.
Name it, then build it
Name each triad: its 3rd, its 5th, then its quality. Then build triads above a given root: the letters are fixed, so choose only the accidentals.
Practice on paper
Free printable worksheets on this topic, each with an answer key.
A chord of three notes stacked in thirds: the root, the 3rd and the 5th. Written on the staff, the three notes sit on three lines in a row or three spaces in a row.
What are the four types of triads?
Major (major 3rd, perfect 5th), minor (minor 3rd, perfect 5th), augmented (major 3rd, augmented 5th) and diminished (minor 3rd, diminished 5th).
How do you tell a major triad from a minor triad?
Look at the middle note. Compare it with the 3rd of the root’s major scale: if it matches, the triad is major; if it is a semitone lower, it is minor. C–E–G is major, C–E♭–G is minor.
What is a diminished triad?
A triad with a minor 3rd and a diminished 5th: both upper notes are a semitone lower than in the major triad. B–D–F is B diminished, written B°.
What is an augmented triad?
A triad with a major 3rd and an augmented 5th: the 5th is a semitone higher than in the major triad. C–E–G♯ is C augmented, written C+.
What are the triads in a major key?
Built on each degree of the scale: I major, ii minor, iii minor, IV major, V major, vi minor and vii° diminished. In C major: C, Dm, Em, F, G, Am and B°.
What are the primary triads?
The triads on degrees 1, 4 and 5 (I, IV and V): the tonic, subdominant and dominant. In a major key they are all major, and together they harmonise most simple melodies.
Learn it properly
The course teaches triads in 2 video lessons with practice questions, graded quizzes and printable sheets.
