How does a through-composed melody differ from a melody built from repeated phrases?

In the context of musical sound, the primary difference between a through-composed melody and one built from repeated phrases lies in the presence or absence of a repetitive structural plan.1

Through-Composed Melodies

A through-composed melody is characterized by the continuous presentation of new melodic material. In this approach, there is no repetitive plan; the structure typically follows a sequence—such as a-b-c-d—where each section introduces fresh musical ideas rather than returning to or restating previous ones. While some through-composed works may use a consistent rhythmic pattern to maintain coherence, they avoid the formal repetition of melodic phrases.21

Melodies Built from Repeated Phrases

In contrast, many musical forms rely on the disposition of structural units—specifically phrases—that are organized through repetition, contrast, or variation. These melodies are often additive and hierarchical, using techniques such as:1
* Repetition: The exact restatement of a phrase.1
* Contrast: The introduction of a completely different phrase.1
* Variation: Altering a phrase while keeping its identity perceptible.1
* Sequence: Repeating a phrase at a different pitch level.13

These methods create a sense of familiarity and formal organization, such as in three-part form, which is common in Western music.1