Sometimes it can be musically interesting to elide one phrase with another. Instead of allowing a phrase to conclude as anticipated, for example on the fourth bar of a four-bar phrase, one can create a moment of surprise by eliding the end of this phrase with the beginning of the next, in effect shortening the first phrase.
Sing through the first two-phrase melody below, noting how the first phrase reaches a natural conclusion in the fourth bar, and the second phrase begins as expected in the fifth. Then, sing through the second melody and compare.
In the second two-phrase melody, note how the anticipated arrival on tonic at the end of the first phrase becomes the tonic beginning of the second phrase. By eliding the end of the first phrase with the beginning of the second, the first phrase in this case becomes truncated to three measures in length, creating a moment of surprise and melodic asymmetry.
Another way to play with expectations of melodic form is to extend a melody beyond its expected conclusion. Sing through the following two-phrase melody:
Notice how the second phrase is longer than expected. The two-bar length of the first phrase set up an expectation of a two-bar second phrase, perhaps something like the following:
In the first example, the second phrase overshoots its expected length by one additional measure. This is an example of a Phrase Extension. Depending on how a phrase is extended, it can fall into one of two types:
1. Pre-Cadential Extension
Notice how the extended phrase in the first example delays the arrival on the tonic, meandering around for a couple more beats before arriving on scale degree 1 a measure later. Because this extension occurs before the conclusion of the final cadence, this phrase can be said to have a Pre-Cadential Extension. Now, compare that extended phrase with the following version:
2. Post-Cadential Extension
In this example, the second phrase ends on the tonic at the expected location, at the conclusion of the implied V7-I cadence on beat two of its second bar. Unlike the first extension example, the phrase could have ended right here, but in this case there is an additional tag at the end reiterating the arrival on the tonic. This is an example of a Post-Cadential Extension.
Here are these two extended phrases side-by side, showing how one is extended prior to the cadence, and the other extended after the cadence: