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An Introduction to Form in Instrumental Music


Musical form is the structure and logic of a piece of music. Under the heading of form you can consider balance, symmetry, proportion, pacing, and other topics related to the overall presentation of your piece.

Form is useful from the perspective of both the composer and the listener. For the composers, form can provide a template for presenting our material. Relying on what has worked for the great composers of the past, we can confidently plan out a satisfying composition. We can also use a knowledge of convention to "break the rules" and do new things.

For the listeners, form gives them a way to understand what is happening in the music. By being able to follow the different sections and actually be aware of changes from one theme to another, they are able to enjoy the music. There is a fine balance between giving the audience what they expect and surprising them, and using form is an excellent way to fulfill or deny those expectations.

Of the countless subjects to study about composing music, I've always considered form to be one of the most overlooked yet important. Although there are many fantastic books about musical form, universities, teachers and students seem to place too little emphasis on the topic.

In this tutorial we're going to talk about the basics of musical form for instrumental music, up to and including the simple ternary.

The A Section

As discussed in a recent tutorial, there are two basic theme types: the sentence and the period. There are also many ways that the sentence and period forms can be combined into something in-between.

The basic sentence or period is typically eight bars long. This alone can actually be enough to constitute an "A" section, or you can double the length to come up with a 16 bar section. An 8 bar or 16 bar A section can be repeated, either exactly or varied, to create a 16 or 32 bar piece of music. If you were writing music for a video game or a commercial, this might be all you need to be considered a complete and satisfying piece of music.

Of course you don't have to write in units of 2, 4, 8, 16 etc. Writing shorter or longer phrases can make your music less predictable and more interesting, or help you either draw a slow theme out or pick up the pace and make a section more exciting.

However I advise you to learn to walk before you run. So although you might feel confident that this stuff is all too easy for you, I assure you that if you force yourself to diligently work on very simple 8/16/32 bar pieces first, you will develop a strong foundation for getting more fancy in the future.

The elegant balance of a 16 bar structure needs to be deeply internalized so that you can truly be aware of how your extensions or cuts affect that balance.

The B Section

In most cases 16 bars isn't going to be enough to create a satisfying piece. You could repeat it, or add superfluous parts like an introduction or and ending, but at some point you are simply going to need more material. That's where the B section comes in.

At it's most basic, the B section is a contrasting segment. Something different to keep things interesting and give us a break from the now familiar A section.

In general, the B section is subordinate to the A. If your A section is the superhero, the B section is the sidekick. It's there to provide support and contrast but not necessarily to steal the show.

Many B sections are looser in structure. While the A section might be a nice sturdy 16 bars, the B section can often be shorter or longer. This uneven length helps support the section's weaker role.

Keep in mind that the term "contrasting" does not mean "completely different". The B section should still feel like it belongs in the same piece of music. In simple pieces very little will change but perhaps the shape of the melody.

The B section should feel like a close sibling to A, not a foreign enemy.

Simple Ternary Form

A ternary form is made up of three parts - A B A.

The most important feature of the ternary is the return to A, with the B section functioning as a contrasting middle.

In ternary forms, the first A section can be complete (end on a perfect authentic cadence) or incomplete (end on a half cadence, modulate to another key, etc.). But the B theme, almost as a rule, is open ended. This is because part of the function of B is to set up a satisfying return to A.

Let's look at an actual piece of music.

In this short piece by Schumann, there are several things to look out for:

  • An A section that is a simple eight bar sentence.
  • An exact repetition of A.
  • A contrasting B section. It contrasts by starting in Em instead of G, has a different (and simpler) melodic shape, is an unbalanced 6 bars in length, and ends hanging unresolved on a fermata with the third in the melody instead of tonic.
  • Return to A.
  • An exact repetition of B-A.


As a very general rule of thumb, we can tolerate one exact repetition before it starts to become boring. So you can say something, say it again, but then it's time to say something else. In the Schumann example above, he repeated A, but he also repeated the last B-A.

Because of how the complement each other with the open/closed or unresolved/resolved balance, B-A can be thought of as its own complete unit. So Schumann is essentially repeating the first (A) half once, and the second (B-A) half once. What we end up with is a form the looks like AA BA BA, which has some nice features to it.

The piece is three times longer than the two sections that make it up. So if your A and B sections were both 8 bars, this is an easy way to turn 16 bars of music into 48. Or to turn 30 seconds of music into 90.

Extra Segments

Without disrupting the overall balance and proportion of the ternary form, you can include extra little appendages like introductions, interludes and codas.

These should be kept simple so that they don't compete for space as a main section. Usually this means they don't feature a prominent melody or theme and are made up of repetitive figures.


Tetris A Theme

Basic structure - A B A:

  • A - 8 bar theme based on period form.
  • Repetition of A.
  • B - contrasting 8 bar section. Different and simpler melody, ends on a half cadence.
  • Return to A exactly as before.
  • At this point, the repetitions go on infinitely because it's continuous video game music.

Crystal Eye Castle - Lorne Balfe

Basic structure - Intro A B A B interlude A B Coda:

  • Intro - 4 bar simple, non-thematic section.
  • A - 12 bar theme. Feels balanced because it is four units of three bars, much like an 8 bar theme is four units of 2 bars.
  • B - contrasting theme, less balanced 10 bars.
  • Return to A.
  • Repetition of B.
  • Interlude - 4 bar drum break which creates an interesting contrast, fills in time, and sets us up for a bigger A.
  • Return to A - varied with bigger drums.
  • He includes one last repetition of B.
  • Outro - repeating figure with very simple texture, no melody.

Anakin's Theme - John Williams

I use this piece very often on Tuts+ because you can learn something from it at every angle!

Basic structure - Extended Intro A B A Coda:

  • Intro - two parts (see this tutorial for more information).
  • A - 8 bar period theme.
  • B - contrasting theme. Change in texture, 12 bars in length, ends on half cadence.
  • Return to A. Varied, with more intensity and passion. Also note a repetition of the last four bars.
  • Outro - an extended coda that progressively simplifies the material and thins out the texture.

A Word About Film Music

Although we are focussing on instrumental music, I caution you—when listening for examples of your own—to be conscientious about film music. Most cuts on a soundtrack are written to be heard with the picture, not to be listened to independently. The "form" of the film is what takes precedence, not the form of a listenable piece of music.

If you want to practice listening for the basic elements of form, you will probably do best listening to jazz or 18th and 19th Century classical. If you insist on listening to film music, try to listen to main titles or themes; essentially, pieces of music that were intended to be listened to as opposed to underscore.


From listening to and analyzing the three examples above, what I particularly want you to take away from this is how you can put together these basic structural elements in very simple ways and still come out with a great piece of music.

Even the most complex 20th Century music can often be distilled into the basic ternary form, and the more aware of it you are the more you'll begin to hear it everywhere. (Rule of Three, anyone?)

I encourage you to take the simple ABA form and run with it. Learn to hear it in other music and learn to take advantage of this proportion and balance it provides you. Share your discoveries in the comments!

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