Music Theory
Acoustic Composition
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How Does Musical Form Work?

In music theory and composition, form refers to the structure of a piece. Since music is a temporal art form (it happens over a duration of time), the order in which ideas are presented is of the upmost important. Music theory students tend to spend a large portion of their early studies on how musical form works on small and large scales. Here are some important terminology in the study of musical form:

  • Phrase – A phrase is the smallest section of musical form. It typically consists of 4-8 measures and ends with a cadence, or resting point. It’s the smallest section of music that gives the impression of a complete thought.
Here’s a phrase from the popular Irish tune “Danny Boy,” notice how it ends on a half note on the second scale degree. This is implying either a dominant or subdominant harmony, in this case, it’s usually treated as a dominant harmony which would make this a half cadence (we’ll discuss cadences further in a future lesson on harmony).
  • Sentence – A sentence is a type of phrase with a specific structure. It begins with a melodic motive that is then repeated or transposed to a different pitch and then followed with a different idea ending in a cadence.
This original melody is an example of a sentence. Notice that the first two measures look nearly identical even though they contain different notes. This is an example of sequencing (or transposing) where the intervals between the notes are preserved although the notes change. Following this is unrelated material that brings the melody to close on the tonic.
  • Period – A period consists of two or more phrases that are strung together with the strongest cadence occurring at the end of the final phrase. Periods are typically eight or more measures long.
Here’s the first period of “Danny Boy” notice that it contains the first phrase we already looked at, followed by a near repetition, but then concluding with a slightly different phrase that concludes on a half note on the first scale degree.

Now that we understand how to breakdown smaller sections or periods, how do we go about distinguishing and labeling these different periods?