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--G, a major third and a perfect fifth. Therefore, the triad is major.




The second triad is D--F--A, a minor third and a perfect fifth. Therefore, it is minor.




The third triad is E--G--B, a minor third and a perfect fifth. Therefore, it is also minor.




The fourth triad is F--A--C, a major third and a perfect fifth. Therefore, it is major.




The fifth triad is G--B--D, a major third and a perfect fifth. Therefore, it is also major.




The sixth triad is A--C--E, a minor third and a perfect fifth. Therefore, it is minor.




The seventh triad is B--D--F, a minor third and a diminished fifth. Therefore, it is diminished.




The eighth triad is a repetition of the first (C--E--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, stack two generic thirds.




Finally, let's analyze the resulting triads.




The first triad is C--Eb--G, a minor third and a perfect fifth. Therefore, the triad is minor.




The second triad is D--F--Ab, a minor third and a diminished fifth. Therefore, it is diminished.




The third triad is Eb--G--Bb, a major third and a perfect fifth. Therefore, it is major.




The fourth triad is F--Ab--C, a minor third and a perfect fifth. Therefore, it is minor.




The fifth triad is G--Bb--D, a minor third and a perfect fifth. Therefore, it is also minor.




The sixth triad is Ab--C--Eb, a major third and a perfect fifth. Therefore, it is major.




The seventh triad is Bb--D--F, a major third and a perfect fifth. Therefore, it is also major.




The eighth triad is a repetition of the first (C--Eb--G), making it minor.




Next, 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--B, a major third and an augmented fifth. Therefore, it is augmented.




The fifth triad is now G--B--D, a major third and a perfect fifth. Therefore, it is major.




The seventh triad is now B--D--F, a minor third and a diminished fifth. Therefore, it is diminished.




Finally, we will discuss the diatonic triads of melodic minor.