I thought I would share this article about how when writing music, it can be helpful to think about your bass-line as a “second melody”. If the composer is careful in noticing the relationship between the two, the song will be more dynamic and engaging. There are 4 different ways to asses this relationship between the motion of the melody and the motion of the bass: parallel, similar, oblique, contrary. Each describes a relationship between the chord structure and the direction of movement of the line. Variety between the 4 creates complex, exciting pieces like the classical composers did.
Worth your attention:
The Relationship Between Melodies and Bass Lines