Phrase

Often, musicians use the term "phrase" to refer to any group of notes grouped together in some sort of meaningful way -- e.g. a group of notes under a slur, or a group of notes performed in a single breath, or a group of notes that are bowed together. Our definition of "phrase" is a bit more formal than these.

A phrase is a unit of musical meaning that ends in a cadence.

If a passage does not end in a cadence, it is not a complete phrase.

Since our study of tonal form is largely guided by our perception of where cadences occur and how they relate to one another (and to the tonic), we might say that a phrase is a cadence's way of getting to the next cadence.

Good performers play or sing phrases, not single notes; likewise, good analysis deals with phrases, not chords. Phrases are to chords or notes as molecules are to atoms.

The rate at which phrases succeed one another is called phrase rhythm.

Sentence

An eight-measure phrase built out of three sub-phrases whose durations are 2 bars, 2 bars, and 4 bars.

The first two sub-phrases present an initial idea, and are motivically similar; the final sub-phrase provides continuation and leads to a cadence.

a	a'	b
2 measures	2 measures	4 measures

Note that the first two sub-phrases end not with a cadence, but with a caesura. The sentence is thus a single phrase, not a period. The cadence at the end of the period can be either authentic or half.