An alternative to thinking about such phrases as a tune plus chords is to consider the bass line as a melody. In a short phrase that begins and ends on the tonic, the bass line can be thought of as line that fills in the gap between the first tonic (I) and the dominant (V) of the final perfect cadence. Below are a few patterns that fill in the gap in this way. The first example fills the gap with an ascending arpeggio and the second with an ascending scale:

Here is the simplest way of filling in the gap with a scale. The bass line consists of a quaver scale. Harmonically the result is a first inversion tonic chord between I and V (shown in brackets).

The next example is a little more complicated. All the steps of the rising scale from the model at the top of the page are given their own harmony. In addition, there is a leap back to the tonic in just before the b flat on the first beat of the last bar.

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