Triad Chords
Senior 3 · Music
Triad Chords
Lesson 2 of 4
30 min
Play C–E–G, then lower the middle note by one semitone to E♭ and play C–E♭–G. The letters are the same, the root is the same, yet the second chord sounds darker. Musicians call that difference the quality (or type) of a triad. It depends only on the size of the two thirds, so before you can name a triad you must be able to measure a third.
In S1 you measured intervals in semitones on the keyboard: one semitone is the step from any key to the very next key, black or white. A third from a root always spans three letter names, but it can be two different sizes.
Definition
Major third: a third that spans 4 semitones. Example: C to E (C–C♯–D–D♯–E).
Minor third: a third that spans 3 semitones. Example: C to E♭, or E to G.
Quality of a triad: its type, major, minor, diminished or augmented, fixed by the sizes of its two thirds. Chord symbols show it: C (major), Cm (minor), C° or Cdim (diminished), C+ or Caug (augmented).
Stack two thirds and there are only four ways to combine them. Each combination is one quality of triad.
| Quality | Lower third (root to third) | Upper third (third to fifth) | Root to fifth | On C | Symbol |
|---|---|---|---|---|---|
| Major | major, 4 semitones | minor, 3 semitones | perfect fifth, 7 | C–E–G | C |
| Minor | minor, 3 semitones | major, 4 semitones | perfect fifth, 7 | C–E♭–G | Cm |
| Diminished | minor, 3 semitones | minor, 3 semitones | diminished fifth, 6 | C–E♭–G♭ | C° |
| Augmented | major, 4 semitones | major, 4 semitones | augmented fifth, 8 | C–E–G♯ | C+ |
Major and minor triads share the same outer fifth (7 semitones); only the middle note moves. Diminished and augmented triads change the fifth: the diminished fifth is squeezed to 6 semitones and the augmented fifth stretched to 8. Many listeners describe major triads as bright, minor as darker, diminished as tense and augmented as strange or unfinished; listen and decide for yourself.
Worked example 1: name the quality of D–F–A
Worked example 2: build a major triad on D, then an augmented triad on F
Video: "Music Theory: Building Triads (Major, Minor, Diminished, Augmented)", Scott Watson. Dr Watson builds all four qualities from their thirds. Pause after each one and check it against the recipe table above.
Tip
Four words, four recipes. Major = big then small (4 + 3). Minor = small then big (3 + 4). Diminished = small, small (3 + 3). Augmented = big, big (4 + 4).
Warning
Common mistakes. (1) Counting the starting key as "1": count the steps you move, not the keys you touch; C to E is 4 steps. (2) Changing the letters to fit the sound: D major is D–F♯–A, never D–G♭–A, even though F♯ and G♭ are the same key. A triad always keeps its every-other-letter spelling.
Practice
Remember
Sources and credits
