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What Is a Triad? Scale Degrees and Chords
Recall that the term “scale degree” refers to the designation of the notes of a major or minor diatonic scale using numbers: 1, 2, 3, 4, 5, 6, 7, and 1 (8), where 1 is the tonic note of the scale, 7 is the leading tone, and so on.
A triad is a chord comprised of three of those numbered scaled degrees, namely, scale degrees 1, 3, and 5.
It turns out that most of the strong overtones—1st, 2nd, 3rd, 4th, 5th, 7th, and 9th—of a given fundamental tone (scale degree 1) correspond to the pitches associated with scale degrees 1, 3, and 5 of the major diatonic scale (Table 33 below). And when you play these three scale degrees—1, 3, and 5— simultaneously, you get a chord called a triad.
TABLE 33 Fundamental and First 9 Overtones of the Tone “C”
| Tone / Overtone | Multiple of Fundamental | Freq.Ratio | Associated... | Consonant/Dissonant | |
|---|---|---|---|---|---|
| Scale Degree | Note | ||||
| Fundamental | 1 (f) | 1 : 1 | 1 | C | Consonant |
| 1st Overtone | f x 2 | 1 : 2 | 1 | C | Consonant |
| 2nd Overtone | f x 3 | 2 : 3 | 5 | G | Consonant |
| 3rd Overtone | f x 4 | 1 : 2 | 1 | C | Consonant |
| 4th Overtone | f x 5 | 4 : 5 | 3 | E | Consonant |
| 5th Overtone | f x 6 | 2 : 3 | 5 | G | Consonant |
| 6th Overtone | f x 7 | 5 : 9 | ♭7 | B♭ | Dissonant |
| 7th Overtone | f x 8 | 1 : 2 | 1 | C | Consonant |
| 8th Overtone | f x 9 | 8 : 9 | 2 | D | Dissonant |
| 9th Overtone | f x 10 | 4 : 5 | 3 | E | Consonant |
When you play the notes C, E, and G (scale degrees 1, 3, and 5) simultaneously on your guitar or piano, you hear a beautiful harmonic sound. It’s called the major triad because it consists of three notes (scale degrees 1, 3, and 5) of the major scale. Specifically, it’s the C major triad or C major chord.
This simple triad forms the basis of all harmony in the Western tonal system.