Chapter 6 of the Roig-Francoli lays out the material fairly well. I’m going to put it a bit more hierarchically.
At the smallest levels of organization you have motives and phrase segments (sub-phrases). Motives are the smallest recognizable musical elements, with identifiable rhythmic or rhythmic and melodic characteristics. You recognize motives partly by their repetition and development. Think Beethoven’s Fifth Symphony. Not all music makes use of motives, or motivic development. Phrase segments are units of phrases, most often found in sentence structure, but sometimes just dividing a phrase in half.
Phrases are complete melodic and harmonic statements. By complete, I mean that they end with a cadence and usually some sort of melodic/rhythmic stoppage. Remember that half cadences end on the dominant triad (V), not the dominant seventh chord (V7).
Sentence structure is built upon phrase segments. The form is a + a’ + b, in the proportion 1 + 1 + 2. The phrase handout outlining Schoenberg/Caplin ideas calls the structure basic idea, repeat of the basic idea with some variation (usually transposition), contrasting idea.
Sometimes one phrase will end at the same point that another phrase begins. This overlap of ending and beginning is called an elision. With an elision, it is possible that two four-measure phrases will only take up seven measures of music.
Phrases can be organized into group relationships. If two or more phrases show a weak – strong relationship we can talk about these phrases forming a period. A period is generally formed by two phrases in an antecedent – consequent relationship. The antecedent phrase has a weaker cadence than the consequent phrase. Usually the relationship is half cadence to perfect authentic cadence. The IAC to PAC relationship happens less frequently.
Period relationships in classical music are most often in the form of a parallel period. A parallel period has two phrases that begin with the same melodic and harmonic material (usually the first two measures) before diverging to end with different cadences. Contrasting periods (phrases start with different material) are found less often, but can occur in some earlier classical composers (Hadyn, for example) and Baroque composers.
Periods can sometimes be three phrases, with two antecedent phrases and one consequent phrase. You can also find double periods, with the first and third phrase being the same, and the second phrase having a weaker cadence than the fourth. Modulating periods will often be parallel in form, ending the first phrase on a HC, and the second phrase with a PAC in a new tonal area. In major keys, almost always the PAC will be on the fifth scale degree. In minor keys the PAC will usually be on the third scale degree (the relative major).
Phrases that don’t form period relationships, but still go together musically, are called phrase groups.
Phrase diagrams will show phrase marks/slurs for each phrase; phrase labels designating the phrase relationships (a, a’ for parallel periods; a, b for contrasting periods, indicating relationship of melodic material); a period marking/slur if a period is present; measure numbers for the start of each phrase, and the end of each phrase; the key the music is in; and each cadence will be labeled as for type. If there is a modulation, your diagram will indicate that as well.
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