The note for composition has its own direction. The C note is following the sound notes for C key(CDEFGABC) notes. And C key notes are melody for C chord. So C,E,G notes are basic stem bass sound for the melody and its own direction for melody. C,E,G notes of C major, C key melody are fit to C chord. When the bass sound ( It is C chord for melody.) C,E,G for the composition, then we use C bass note fit to the notes C,E,G soprano in melody.(Puzzle to fit) So when we change The C chord(C major, C key) to F sound in melody, then the bass chord is F and the soprano notes are F,A,C that is fit to F chord(C key) in bass. And it can be played with G chord(G bass note for C key)-It can be D,E,A,B chords. Finally it is finished by C note( in soprano melody) at the end phrase of the song composition.