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The plagal cadence is a fundamental musical phrase that has been used extensively in Western music, especially in religious and hymnody contexts. It provides a sense of resolution and calmness, often heard at the end of hymns and spirituals. Understanding its intervallic structure is key to appreciating its unique sound and function.
What Is a Plagal Cadence?
A plagal cadence occurs when the IV chord (subdominant) moves to the I chord (tonic). Unlike the more conclusive perfect authentic cadence, the plagal cadence has a softer, more meditative quality. It is often called the “Amen” cadence because of its frequent use at the end of hymns where the word “Amen” is sung.
Intervallic Components of the Plagal Cadence
The core of the plagal cadence lies in the relationship between the IV and I chords. These chords are built on specific intervals that give the cadence its characteristic sound. The key intervals include:
- Fourth: The movement from the IV to the I chord involves a perfect fourth interval between the roots.
- Subdominant to Tonic: The IV chord (built on the fourth degree) contains the notes F-A-C in C major, leading to the I chord notes C-E-G.
- Shared Notes: The note C is common to both chords, providing smooth voice leading.
Intervallic Movement Within the Chords
Within the chords, the intervals are also significant. The IV chord typically features:
- F to A: a major third
- A to C: a minor third
Moving to the I chord, the notes form:
- C to E: a major third
- E to G: a minor third
Conclusion
The plagal cadence’s distinct intervallic structure—centered around the movement from the subdominant (IV) to the tonic (I)—creates its characteristic sound. The perfect fourth interval between the roots, combined with shared notes and internal thirds within the chords, contributes to its gentle, resolved quality. Appreciating these intervals enhances our understanding of how composers craft emotional and spiritual musical moments.