Parallelism in music theory refers to a fundamental compositional technique where two or more distinct melodic lines or "voices" move simultaneously in the same direction, consistently maintaining the same interval relationship between them.
Understanding Parallelism
At its core, parallelism describes a specific type of voice leading where multiple parts move together. In music, this concept is formally known by several terms, including parallel harmony, harmonic parallelism, harmonic planing, or parallel voice leading. As defined, it is the parallel movement of two or more melodies. This means that if one voice moves up or down by a certain interval, the other voices also move in the same direction by the same type of interval, preserving the initial harmonic distance.
Key Terminology
The concept of parallelism has various names that describe the same fundamental idea:
| Term | Description |
|---|---|
| Parallel Harmony | General term referring to the simultaneous movement of voices maintaining a consistent interval, often implying the chords formed by these voices also move in parallel. |
| Harmonic Parallelism | Emphasizes the harmonic result of the parallel motion, where entire chord structures might shift while keeping their internal intervals consistent. |
| Harmonic Planing | Particularly used to describe a technique where entire chords (often non-functional, i.e., not following traditional root progressions) move in parallel steps, creating a floating quality. Often associated with Impressionistic music. |
| Parallel Voice Leading | Focuses on the individual melodic lines (voices) and how they move in relation to each other, maintaining constant intervals. |
How Parallel Movement Works
When voices move in parallel, they essentially "shadow" each other. For instance, if you have a melody in the treble and another below it a perfect fifth away, parallel movement would mean that as the top melody moves up a step, the lower melody also moves up a step, ensuring it remains a perfect fifth below. This consistent interval maintenance is what defines parallel motion.
Types and Contexts of Parallelism
The use and acceptance of parallelism in music theory have varied significantly across historical periods and compositional styles.
Acceptable vs. Forbidden Parallels
Music theory, particularly in the common practice period (roughly 1600-1900) and strict counterpoint, distinguishes between different types of parallel intervals:
- Perfect Parallels (Octaves and Fifths): In traditional Western part-writing rules, parallel octaves and parallel fifths were generally forbidden.
- Parallel Octaves (e.g., C-C moving to D-D) are avoided because they cause two voices to lose their independence, effectively reducing the number of independent parts.
- Parallel Fifths (e.g., C-G moving to D-A) were largely prohibited because they were believed to create a hollow sound, dilute harmonic progression, or make the music sound archaic (reminiscent of medieval organum where they were common).
- Imperfect Parallels (Thirds and Sixths): Parallel thirds and sixths, on the other hand, are widely used and encouraged. They create a rich, consonant sound and are fundamental to much of Western harmony, adding fullness without sacrificing voice independence.
Common Examples in Practice
Parallelism can be observed in various musical contexts:
- Chorales and Hymns: Often feature parallel thirds and sixths to create a full, consonant sound, particularly in SATB (Soprano, Alto, Tenor, Bass) arrangements.
- Impressionistic Music: Composers like Claude Debussy and Maurice Ravel frequently employed harmonic planing (parallel chords, often ninth or eleventh chords) to create atmospheric and coloristic effects, intentionally moving away from traditional functional harmony.
- Rock and Pop Music: Parallel fifths are commonly used in power chords (e.g., C-G-C' or C-G-E') in rock and metal to create a powerful, driving sound, demonstrating a deliberate departure from classical prohibitions.
- Medieval Organum: One of the earliest forms of polyphony, where two voices would move predominantly in parallel perfect fourths or fifths.
Significance in Music Composition
Parallelism plays a crucial role in shaping the texture, sonority, and expressive qualities of music. It can:
- Create Unity: By moving together, voices can emphasize a single melodic idea or harmonic progression.
- Add Richness: Parallel imperfect intervals (thirds, sixths) provide a lush, consonant sound.
- Generate Specific Colors: Harmonic planing creates unique, often ethereal or bold, soundscapes distinct from traditional functional harmony.
- Direct Flow: The consistent movement can give a strong sense of direction to the music.
Understanding parallelism is essential for analyzing musical structures and appreciating how composers manipulate voice leading to achieve desired sonic effects.
