The Rules for Writing Four-Part Music

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  • 0:04 Writing Four-Part Music
  • 0:51 Know Your Lines
  • 1:39 Rules of Motion
  • 3:22 Relationships and Resolutions
  • 4:57 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Four-part writing can be difficult, but you don't have to reinvent the wheel. In this lesson, we'll look over some common rules to make four-part writing a little easier.

Writing Four-Part Music

There was once a king who decided to divide his land between his four children, each of which would start their own royal line. He could have simply let them negotiate between each other without any guidance, but instead he gave them rules. They could not invade each other's land, they could not do the exact same thing with their land as their siblings, and they were not allowed to marry between their families. The four children followed the rules, and there was harmony between their four lines.

The old king wanted harmony, and as a composer, so do you. The only difference is that you presumably don't have an entire kingdom to give away. Instead, you have four lines of music. Four-part music can be tricky to compose, and if one line is awry then the entire piece can feel chaotic and discordant. So, be like the old king. Rules are what keep four individual lines working together in total harmony.

Know Your Lines

In this lesson, we're going to cover seven essential rules for writing four-part music, and it all starts with knowing your four lines. So, here we go.

Rule #1: Know the vocal ranges

Four-part music is traditionally divided into soprano, alto, tenor, and bass (ranging from highest to lowest, respectively). Each lines has its own natural range, and you should strive to keep the notes for each line within the heart of that range.

Why is it so important to understand these natural ranges? It's because of:

Rule #2: Write for four individual lines

Four-part music is defined by the ability to distinctly recognize four individual voices, and keeping each within a different range is essential to accomplish this. When you write each line in the notes that overlap, you run the risk of losing the distinction of four voices.

Rules of Motion

So, how do you keep each line independent? Besides staying in the range of each line, the four voices get their character from motion, or the ups and downs and relationship to the other lines.

Rule #3: Motion is key to successful counterpoint

If you want all four lines to sound distinct but still sound good, they have to keep moving. If one line plays the same note for too long, it becomes boring very quickly and loses its character. So, keep lines active.

With this being said, there are some important rules about what kind of motion is not allowed. Your four voices are defined by their ranking of highest to lowest. The soprano is the highest voice, so the notes in the soprano line should always be highest, just as the notes in the bass should always be lowest. Don't mix this up.

Crossed voices occur when the lines switch order within the same chord, while overlapping voices switch lines between two chords. In both cases, the normal order is thrown off. For example, imagine a chord where the alto was higher than the soprano, or the tenor was lower than the bass. This sort of motion blends the lines, and the result is that they lose their individual distinction.

Another way to blur lines and lose a clear four-part harmony is through parallel motion, which is what happens when two lines move at the same interval. There are times when this can be done, but it's tricky and risky. However, it should absolutely never occur with parallel fifths and parallel octaves. If one line moves by a fifth, no other line should. Parallel fifth and octaves blend too harmoniously, and as a result you lose any distinction between the lines.

So, what's the rule here? Don't do these things:

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