Melody, harmony and rhythm are the materials. Form is the architecture: how a piece is laid out in time so that a listener can find their way through it. Orchestration is the paint: which instruments carry each line. This final level brings everything together.

Repetition, contrast and return

Musical form is the overall structure of a piece: how its sections are arranged, repeated and contrasted. Because music passes in time and cannot be seen all at once, form depends on memory. Repetition lets us recognize; contrast keeps us interested; return gives a sense of homecoming. Analysts label sections with letters. A is the first idea, B is something different, and a return to the first idea is A again.

The simplest form is strophic, in which the same music repeats for every verse while the words change. Most hymns and many folk ballads work this way. Binary form has two contrasting sections, AB, and was common in dances of the 1700s. Ternary form is ABA: a section, a contrasting middle and a return of the first. Many minuets and lullabies follow it, and the return of A feels like waking up somewhere familiar.

Song forms

Popular songs use a handful of reliable plans. The great American songs of the 1920s to 1950s often follow a 32-bar form, AABA: a main tune twice, a contrasting bridge, then the main tune again. "Somewhere Over the Rainbow" is a well known example. Since the 1960s, much pop has used verse and chorus. In verse-chorus form, the verses change their words while the chorus repeats both its words and its music, so the chorus becomes the part everyone sings along to. A bridge, a section with new material, often appears once near the end to refresh the ear before the last chorus. The twelve-bar blues from the sixth level is also a form: each twelve-bar cycle is a chorus, repeated with new words or new solos.

Classical forms

Larger works use more elaborate designs. In theme and variations, a tune is stated and then repeated many times with changes to its rhythm, harmony, mood or decoration. Mozart wrote a set on the French melody known in English as "Twinkle, Twinkle, Little Star." A rondo brings back a main section again and again between contrasting episodes, as in ABACA. The cheerful returns make rondos common as final movements, and Beethoven's "Für Elise" is a familiar example.

The most important large form of the classical era is sonata form, used for the first movements of countless symphonies, sonatas and string quartets by Haydn, Mozart, Beethoven and their successors. It has three main parts. The exposition presents two contrasting themes, the second in a new key. The development breaks those themes into pieces and pushes them through restless keys. In the recapitulation, the themes return, now both in the home key, resolving the tension the exposition created. The first movement of Mozart's Eine kleine Nachtmusik of 1787 shows the plan clearly.

Orchestration

A melody played on a tuba and the same melody on a piccolo are, in pitch and rhythm, the same tune, yet they hardly feel like the same music. That is timbre at work, and choosing timbres is a craft of its own. Orchestration is deciding which instruments play which parts. The Western orchestra groups its instruments into four families. The four families of the orchestra are strings, woodwinds, brass and percussion. Strings, such as violins and cellos, form the core and can play softly for long stretches. Woodwinds, such as flutes, oboes, clarinets and bassoons, add distinct colors and often carry solo melodies. Brass, such as trumpets, horns and trombones, bring power and brilliance. Percussion adds rhythm, accent and sparkle.

Orchestrators double lines, giving a melody to violins and flutes together for a blended color, or set one solo instrument against a quiet background so it stands out. The same choices apply to rock bands, gospel choirs and electronic producers, who orchestrate with guitars, voices and synthesizers.

Worked example: Ravel's Boléro

Maurice Ravel's Boléro, first performed in Paris in 1928, is almost a laboratory demonstration of orchestration. A snare drum taps out a single rhythm, quietly, and keeps it going from beginning to end. Over it, a flute plays a long, winding melody. Then a clarinet repeats it. Then a bassoon, then other woodwinds, then a muted trumpet, then saxophones, and on through the orchestra. Ravel's Boléro repeats essentially one melody while the orchestration keeps changing.

The harmony barely moves, and the tempo stays steady. What grows is color and weight: Ravel combines instruments in unusual pairings, at one point layering horn, celesta and piccolos so that they blend into what sounds like a new instrument, a trick that relies on the overtone series from the first level. The music swells for about a quarter of an hour, and then, near the very end, it lurches into a new key for a few bars, the only modulation in the piece, before collapsing in a crash. Ravel himself reportedly called it an experiment. Listening to it with this course in mind, you can hear form, rhythm, harmony and timbre each doing their separate jobs, and you can begin to hear any music in the same layered way.