In music theory, two notes played at the same time make an interval, and three or more notes played at the same time make a chord.
Major and minor chords are made up of intervals called thirds, which are formed when you play two notes of a scale that are separated by one note. For example, a C-major scale is made up of the notes C, D, E, F, G, A, B, C. If you play the notes C and E together, omitting the D in between, you have a third. Playing D and F together or E and G together also make thirds, and so on.
A triad is a three-note chord made of the first, third, and fifth notes of the scale. In the case of our C-major scale, the C-major triad is made of the notes C, E, and G. And you'll remember from above that the blow notes on the C diatonic harp are C, E, G, C, E, G, C, E, G, C.
So how convenient is that? Any three adjacent holes you blow together on the C diatonic harmonica form a C-major triad, each with different voicings.
The notes of chords can be played in different orders, and the order of notes in a chord is known as the chord's voicing. For example, the same C-major triad can be voiced, from lowest note to highest, either C-E-G, E-G-C, or G-C-E.
Playing three adjacent draw notes on the harmonica also creates triads. Playing holes 1-2-3 draw forms a G-major triad, as does playing 2-3-4 draw. Other triads formed by adjacent draw notes are:
3-4-5 draw = G7 sound (would be a full G7 with the 2 draw added)
4-5-6 draw = D minor
7-8-9 draw = G7 sound
8-9-10 draw = D minor
FIGURE 2-5: Example of a C-major chord
In the next chapter you'll learn about rhythm and the important part it plays in learning to play the harmonica.