Bass Line
When we harmonise a melody and select chords with specific inversions, the end result is a bass line. For example, choosing the following chords/inversions to harmonise this C major scale will create the bass line shown:
Bass lines tend to follow some typical patterns. Following these patterns will help you to write a convincing sounding bass line.
Moving to a root position chord
Root position chords can be approached by a bass movement of a step (2nd) or a leap (3rd, 4th, 5th).
A leap of a 3rd downwards to a root position chord works better than a leap upwards. (This is because when the chords move downwards, the second bass note does not belong to the previous chord. When the chords move upwards, the second bass note was a part of the previous chord, so the difference between the chords is less easy to perceive.)
Moving to a first inversion chord
First inversion chords are normally approached by a bass movement of a 2nd or a 3rd. We do not often see first inversion chords approached by a 4th or 5th.
If the bass line moves up or down by an interval of a 3rd, the mostly common “progression” is the same chord in a different inversion (which is not really a progression at all, since fundamental chord does not change). This often works well when there is also a skip of a third in the melody line. Here are some examples:
Moving to a second inversion chord
Second inversion chords are normally only used in specific places – the cadential 6/4 or passing 6/4 are the most common. The most common bass movement into a second inversion chord is by step.
Bass line melody
Typically, a bass line is made up of a combination of leaps and steps. It is a good idea to avoid multiple leaps in the same direction, especially when the notes do not belong to the same chord: change direction after a leap if the harmony changes.
Bass lines tend to change direction quite a lot, as this bass line from the opening of Bach’s Chorale 101 illustrates:
