2. Cadences, Phrases, and Periods
A musical work can be divided into sections. The organization of these sections defines the form of the piece. To identify the sections, we need to know where each section begins and ends. A cadence is like the punctuation mark that creates the sense of closure at the end of the section. In analysis of tonal music, a cadence is an important harmonic configuration that provides obvious and precise information involving rhythmic and melodic materials (such as a tonic soprano ending in a strong beat) to facilitate delineation of the piece.
A phrase is a basic section usually ending up with a cadence. The cadence’s function is to inform the listener that a phrase is finished.
Two or more phrases create a period. Differentiating from a phrase, a period has a strong sense of closure. A phrase may end in one of many cadence types, but a period usually closes with an authentic cadence, which firmly lets the listener know that a large section is finished. If a score were an essay, a phrase would be a sentence and a period would be a paragraph.
There are four types of cadences. Every cadence has a sense of closure, but each cadence weighs differently: Authentic cadence sounds quite final, half cadence sounds paused to wait for the next, deceptive cadence gives a surprising false alarm of the end, and plagal cadence sounds conclusive and natural (it’s also known as the “Amen” cadence).
For more theoretical information about various kinds of phrases and periods, refer to other music theory books.