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Section 25.2 The Four Structural Functions in Music

In the “Structural Functions” chapter of A Practical Approach to the Study of Form in Music, Peter Temko and Peter Spencer enumerate four structural functions.
  1. Expository function
  2. Transitional function
  3. Developmental function
  4. Terminative function

Subsection 25.2.1 Expository Function

Music expressing expository function maintains a stable tonal center and clear melodies, usually with well-defined phrases. The vast majority of the music we encountered in binary and ternary form in the last chapter was expository in nature. Additionally, the primary and secondary themes in a sonata form are usually have expository function. Below is the secondary theme from the first movement of Mozart’s Piano Sonata, K. 333.
Figure 25.2.1. Mozart, Piano Sonata, K. 333, I, Secondary Theme
Notice the perfect authentic cadence that closes off this four-phrase parallel double period within the larger sonata form. Cadences are important demarcations within a form.

Subsection 25.2.2 Transitional Function

Music of transitional function moves from one tonal center to another and often features a contrasting accompanimental texture more rhythmically active than preceding expository material. Tonicizations may also occur within a transition. Transitions are sometimes called bridges. Mozart and Haydn often ended their sonata form transitions with a half cadence followed by a rest to signal that the secondary theme was about to commence. Again, notice the importance of cadences to demarcate the form.
Figure 25.2.2. Joseph Haydn, Piano Sonata in C major, Hob. XVI:35, I.
Figure 25.2.3. Mozart, Piano Sonata, K. 284, I.

Subsection 25.2.3 Developmental Function

Music with developmental function often contains sequences and fragmentation of earlier melodies. In addition, developmental music modulates through multiple keys. Phrase lengths may be irregular and elisions may be used by the composer to keep the listener off balance.
It can sometimes be difficult to distinguish between transitional and developmental music. A development section is typically longer than a transition and therefore will contain more sections of a varying nature and as well as a greater number of modulations.
Examples from a development section can be found in Section 11.1 of this text. Note the fragmentation and sequencing of melodic ideas as well as the different keys expressed in the examples throughout that section.

Subsection 25.2.4 Terminative Function

Terminative function is typically expressed through a rather emphatic alternation of tonic and dominant harmonies, usually to affirm a tonal center. The closing theme of a sonata has terminative function.
Figure 25.2.4. Mozart, Symphony No. 41, K. 551, I., Closing Theme
Figure 25.2.5. Beethoven, Moonlight Sonata, Op. 27, No. 2, III, Closing Theme (1802)
Go to the Practice Exercises at the end of this chapter to practice identifying these four structural functions aurally.