A small ternary phrase is an expansion of a period, which you should write first.
- Exposition – a period as above but can optionally modulate to perf. cadence in
dominant at end of consequent [8 bars]
- Contrasting middle – looser construction, often based on a sequence and/or some dominant preparation (see WCT Fingerprints page for help on these) [4 bars]
- Recapitulation – typically the consequent phrase from the Exposition, but it must end with a perfect cadence in the tonic if it did not the first time [4 bars]
This Mozart Andante from Eine kleine Nachtmusik was the second example on the 8-bar period page and here is extended into small ternary. The recapitulation is simply the consquent phrase from the exposition. The contrasting middle is very simple and basically just hangs around on the dominant (sometimes called standing on the dominant – see WCT Fingerprints).
This second example from Mendelssohn’s Fourth Symphony is similar but with slightly more complex harmony in the contrasting middle – a part-circle of fifths from vi to I in the relative major (F), which is than sequenced up a third to be a circle of fifths in the dominant (A).
NOTE: writing a bass that moves continuously in quavers like this is not easy and you should not attempt it unless you are confident you know what you are doing
Mendelssohn, Symphony No. 4, second movement