The Musical Sentence as Succession of Periods

Definition: The fundamental principle that musical sentences comprise successions of distinct periods, with the theme typically constituting the first period and serving as the synthesis of elements contained within the sentence.

Messiaen's Treatment: Messiaen defines the musical sentence as a succession of periods, with the theme as the synthesis of elements contained in the sentence—it generally constitutes the first period. Sentences can comprise:

• One, two, or three different periods
• Four different periods (square sentence)
• A suite of ornamental variations of a theme and its commentary (Chapter IX reference)
• Plainchant forms (Chapter XII reference)
• Sentences growing or decreasing, with longer and longer or shorter and shorter periods

He notes that one can find infinite forms of diverse sentences. For analytical work, he chooses three characteristic sentences: song-sentence (cited by d'Indy), binary and ternary sentences (discussed in detail in Dupré's Traité d'improvisation).

Modern Context: This represents traditional period-phrase-sentence hierarchy adapted to Messiaen's compositional practice:

Classical formal theory:

• Phrase: Basic melodic unit (typically 2–4 measures)
• Period: Two or more phrases in antecedent-consequent relationship
• Sentence: Larger unit comprising multiple periods

Historical precedents:

• Classical phrase structure: Antecedent-consequent periods (Haydn, Mozart)
• Romantic sentence expansion: Extended periods, asymmetrical structures (Brahms, Wagner)
• Formenlehre tradition: German formal theory systematizing structural archetypes (A.B. Marx, Schoenberg)

Messiaen's approach maintains traditional formal categories while applying them to non-tonal material. His sentences operate through:

• Modal unity: Periods unified by shared mode rather than tonal key relationships
• Rhythmic coherence: Added values, nonretrogradable structures, rhythmic pedals creating temporal unity
• Melodic development: Elimination, interversion, registral change transforming thematic material

The reference to "infinite forms of diverse sentences" acknowledges that these three sentence types (song, binary, ternary) represent archetypes, not exhaustive categories. Actual compositional practice produces hybrid forms, extended structures, and novel combinations.

The invocation of d'Indy and Dupré positions Messiaen within French pedagogical tradition—both were major figures in French conservatory training and composition teaching. This demonstrates that Messiaen's innovations build on systematic formal education rather than rejecting it.

Examples: The principle governs all examples; specific sentence types appear in subsequent sections.