Diatonic Triads

Every major and minor scale has seven special triads, called diatonic triads, which are formed from that scale's notes. To discover the diatonic triads, a three step process must be used.

First, construct the scale. We will be using the C major scale for our first example. Next, stack two generic thirds on top of each note. Finally, analyze the resulting triads.

The first triad is C, E, and G - a major third and a perfect fifth. Therefore, the triad is major. The second triad is D, F, and A - a minor third and a perfect fifth. Therefore, it is minor. The third triad is E, G, and B - a minor third and a perfect fifth. Therefore, it is also minor. The fourth triad is F, A, and C - a major third and a perfect fifth. Therefore, it is major. The fifth triad is G, B, and D - a major third and a perfect fifth. Therefore, it is also major. The sixth triad is A, C, and E - a minor third and a perfect fifth. Therefore, it is minor. The seventh triad is B, D, and F - a minor third and a diminished fifth. Therefore, it is diminished. The eighth triad is a repetition of the first (C, E, and G), making it major. The first triad of a major scale will always be major, the second and third triads will always be minor, etc.

Next, we will uncover the diatonic triads of the C Natural Minor scale. First, the scale is constructed. Notice that we are using a key signature rather than placing the accidentals by each note. Again, two generic thirds are stacked on each note. Finally, let's analyze the resulting triads.

The first triad is C, Eb, and G - a minor third and a perfect fifth. Therefore, the triad is minor. The second triad is D, F, and Ab - a minor third and a diminished fifth. Therefore, it is diminished. The third triad is Eb, G, and Bb - a major third and a perfect fifth. Therefore, it is major. The fourth triad is F, Ab, and C - a minor third and a perfect fifth. Therefore, it is minor. The fifth triad is G, Bb, and D - a minor third and a perfect fifth. Therefore, it is also minor. The sixth triad is Ab, C, and Eb - a major third and a perfect fifth. Therefore, it is major. The seventh triad is Bb, D, and F - a major third and a perfect fifth. Therefore, it is also major. The eighth triad is a repetition of the first (C, Eb, and G), making it minor.

Finally, we will discuss the diatonic triads of harmonic minor. To convert natural minor to harmonic minor, the seventh tone is raised a half step. Therefore, each Bb (the seventh tone of C minor) is raised to a B. Since the third, fifth, and seventh chords have been altered, they need to be reanalyzed.

The third triad is now Eb, G, and B - a major third and an augmented fifth. Therefore, it is augmented. The fifth triad is now G, B, and D - a major third and a perfect fifth. Therefore, it is major. Finally, the seventh triad is now B, D, and F - a minor third and a diminished fifth. Therefore, it is diminished.