2. In a mode tonality, we call the first, fourth and fifth chords positive triads, because the constituent sounds of these three chords contain all the tones in the mode, and the properties of these three chords can best represent the properties of the mode. Because these three chords support the framework of mode in function, we call them positive triads, and these three chords are a mode. There is a relationship between stability and instability, inclination and being inclined, which constitutes the basic function of harmony in natural sound system. Besides the positive triad, other natural chords are called auxiliary triads, and the second, third, sixth and seventh chords are called auxiliary triads.
3. According to the above, we classify all natural chords of a key. There are the first, third and sixth chords in the main function group, the fourth, second and sixth chords in the subordinate function group and the fifth, third and seventh chords in the function group. Brothers and sisters can easily see that some chords have dual functions. Yes, how do we explain them? It depends on the position and chord of this chord in the song. To determine the functionality of chords, the use of auxiliary triads in accompaniment mainly plays an excessive and functional continuation role, making music smoother. I suggest that beginners should not use auxiliary triads at first (especially playing classical hymns), but should first master the playing of positive triads and add auxiliary triads, which will get twice the result with half the effort!