Unit 8 Overview: Modes and Form

7 min read‱march 13, 2023

Sumi Vora

Sumi Vora

AP Music TheoryÂ đŸŽ¶

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8.1: Modes

Modal music is a type of music that is based on a specific mode, rather than a major or minor key. This means that the melody, harmony, and chords are all built around the specific pattern of whole and half steps of the chosen mode. Modal music can have a unique and distinct sound, and it can also create a specific emotional or cultural feel.
Just like minor and Major modes have different sounds and moods, all of the other musical modes also have distinct qualities. 
The seven traditional modes in Western music include:
  1. Ionian: This is the major scale, which consists of a specific pattern of whole and half steps (W-W-H-W-W-W-H). It has a bright and happy sound.
  2. Dorian: This mode is similar to the natural minor scale, but with a raised sixth degree. It has a minor quality with a slight hint of major sound.
  3. Phrygian: This mode is similar to the natural minor scale, but with a lowered second degree. It has a distinct Spanish or Middle Eastern sound.
  4. Lydian: This mode is similar to the major scale, but with a raised fourth degree. It has a bright and dreamy sound.
  5. Mixolydian: This mode is similar to the major scale, but with a lowered seventh degree. It has a dominant quality, often used in blues and rock music.
  6. Aeolian: This is the natural minor scale, which consists of a specific pattern of whole and half steps (W-H-W-W-H-W-W). It has a sad and serious sound.
  7. Locrian: This mode is similar to the natural minor scale, but with a lowered second and fifth degrees. It has a tense and dissonant sound.
Here are the modes based on the C Major key signature:
Modes are always referred to based on the beginning note of their scale. So, even though we might build a Lydian mode using the key signature of C Major, it is F Lydian, because the actual scale in Lydian mode starts on an F. 
If you want to get a feel for what the musical modes sound like, listen to this collection of Gregorian Chants. The Gregorian modes are Dorian, Phrygian, Lydian, and Mixolydian, so you will hear all of these in the pieces.  
It's important to note that modes are not only used in ancient or classical music, but also in other genres such as jazz, folk, and pop music. For example, in jazz, modes are often used as the basis for improvisation and in pop music, they can be used to create a specific mood or atmosphere.

8.2: Phrase Relationships

A phrase is like a musical sentence. A phrase in music is a unit of musical structure that typically consists of a group of notes and rhythms that are played or sung together. A phrase usually has a clear beginning and ending, and is often characterized by a sense of completeness or satisfying resolution. 
In the Baroque and Classical eras, musical phrasing took on a far more structured form – phrases were generally approximately the same length throughout a piece, and phrases were structured in such a way that the ending of a phrase was distinct from the beginning of the next phrase. As music became freer and more expressive in the Romantic and Modern periods, phrase structure also became more ambiguous, and phrases began “running into each other.” 

Phrase Relationships

We can characterize the relationship between two subsequent phrases based on how similar they are to each other. If we have two phrases that sound pretty much the same, we will denote each phrase by the letter a, so we have an a a phrase relationship. 
If the basic structure, melodic, and harmonic ideas in subsequent phrases are repeated, but they are varied noticeably between phrases, then we denote it as an a a’ phrase relationship (read “a a prime phrase relationship”) 
There are many ways to vary a phrase while still maintaining the same basic harmonic structure and melody. The most common way is to add or subtract non-chord tones, decorations, and melodic elements. If the composer wants to add drama and tension between one phrase to the next, then they will add more non chord tones. Conversely, if they want to reduce the tension and excitement, they will use less non-chord tones in the a’ phrase. 
Another way to construct a a’ phrase structure is to transpose the phrase into another key.
Finally, a b phrase structure consists of contrasting phrases. There might be harmonic contrast, but the phrases more importantly have melodic contrast.


Groups of two phrases have a special name in music theory – they are called periods. 
Specifically, a period of phrases is a musical structure that consists of two phrases, usually of similar length and structure, that are balanced and complete each other. The first phrase, the antecedent phrase, sets up a musical idea or question and the second phrase, the consequent phrase, provides a resolution or answer to that idea or question. Together, the antecedent and consequent phrases form a complete musical thought or sentence. 
In order for a group of phrases to be a period, the second phrase must end more conclusively than the first. For example, the first phrase may end in a deceptive cadence or a half cadence, and the second phrase might end in an imperfect authentic cadence, or, the first phrase might end in an imperfect authentic cadence and the second phrase might end in a perfect authentic cadence. 
However, let’s just stick with phrase periods for now. There are several types of periods in music: parallel, contrasting, modulating, asymmetrical, and double periods. 
Of all of the types of periods that you will come across in music theory, the double period is probably the most important to know and remember. A double period is made up of a minimum of four phrases, divided into two groups, the antecedent and the consequent. The first two phrases belong to the antecedent group, while the final two phrases form the consequent group which concludes with a cadence that responds to the less definitive cadence at the end of the antecedent group.
Here are some cadence schemes for double periods:

8.3: Common Formal Sections

Formal Sections in Instrumental Music

The exposition (a.k.a. introduction) is the opening section of a piece of music, typically in a sonata, symphony or concerto, where the main musical ideas and themes are introduced. It is often the first section of a multi-movement work, and sets the stage for the rest of the piece. In the exposition, the composer presents the main melodies and harmonies of the piece, often using contrasting themes to create interest and provide a basis for later development. 
An interlude is a musical piece that serves as a transition or break between two main sections of a larger work, such as an opera, musical, or ballet. It typically provides a contrast in mood, rhythm, or style from the surrounding music, and may serve to mark a change of scene or time. Interludes can be played by a full ensemble, or by a single instrument, and can range from simple chord progressions to complex and fully developed pieces. Usually, an interlude is instrumental (no vocals!) and it will contain an instrumental solo or soli. 
A coda is a musical term that refers to the final section of a piece of music. It is typically a short, conclusive section that appears after the main body of the piece and serves as a closing or concluding section. The coda is used to bring the piece to a satisfying and definitive conclusion, often providing a sense of closure and resolution.
A codetta, on the other hand, is a short, concluding section that appears at the end of a phrase or movement within a piece of music. Unlike a coda, which is typically used to conclude the entire piece, a codetta serves as a concluding section for a specific section within the piece. In many cases, codettas and codas are used together in a piece of music, with codettas serving as a series of mini-conclusions that lead up to the final, conclusive coda. This can help to provide a sense of structure and progression throughout the piece, allowing the listener to follow the music and anticipate the final resolution.

Formal Sections in Choral Music

A bridge is a specific type of interlude that comes before the final chorus of a piece. It is usually characterized as being in vocal music. The bridge that connects two main sections of a song, often the verse and the chorus. It provides a transition or contrast from the rest of the song, typically with a different chord progression, melody, or rhythm. The bridge usually serves to provide a break from the repetition of the verse and chorus and to create tension that leads back to the chorus. It is also used to introduce new musical or lyrical ideas to the listener. 
A verse in music theory refers to a section of a song that typically contains the main lyrics and sets up the background or story for the song. It often has a specific melody and rhythm, but can also be harmonically distinct from the chorus or refrain. The verse is typically repeated a number of times throughout the song, with changes in the lyrics to reflect the progression of the story. 
The verse often leads into the chorus, which is a repeating section of a song that typically features the main melody and lyrics. It is often the centerpiece of a song, and its melody and lyrics are designed to be memorable and catchy. The chorus is typically repeated several times throughout the song and serves to provide contrast to the verse, which typically features different lyrics and a different melody. The chorus and verse together form the structure of most popular songs and can help to convey the central message or emotion of the song.
A refrain is also similar to a chorus, but although a chorus is defined by its harmonic and melodic structure as well as its lyrics, refrains may vary their harmonic progressions and melodies, but the lyrics will be repeated. 
Browse Study Guides By Unit
đŸŽ”Unit 1 – Music Fundamentals I (Pitch, Major Scales and Key Signatures, Rhythm, Meter, and Expressive Elements)
đŸŽ¶Unit 2 – Music Fundamentals II (Minor Scales and Key Signatures, Melody, Timbre, and Texture)
đŸŽ»Unit 3 – Music Fundamentals III (Triads and Seventh Chords)
đŸŽčUnit 4 – Harmony and Voice Leading I (Chord Function, Cadence, and Phrase)
🎾Unit 5: Harmony and Voice Leading II: Chord Progressions and Predominant Function
đŸŽșUnit 6 – Harmony and Voice Leading III (Embellishments, Motives, and Melodic Devices)
đŸŽ€Unit 7 – Harmony and Voice Leading IV (Secondary Function)
đŸŽ·Unit 8 – Modes & Form
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