by Danlee Mitchell and Jack Logan, Ph.D.

There are Three Foundational Procedures in music that are basic to the composing of music. These three foundational procedures are repetition, variation and contrast. These procedures constitute a "method of procedure" for every operational dimension of music. They are foundational procedures seen not only in music but also in other art as well as all aspects of nature.
Composers weave and mold the Eight Basic Elements into small patterns of material which become larger patterns of material that ultimately make up the complete structure of a work. One or more of the Eight Basic Elements functions as "idea" (usually melody) in any given passage, while the remaining elements serve as "accompaniment" to the "idea". Musical structure has various layers of complexity in any composition and these various layers exist in a continuum ranging from the micro (small) level, the mid (intermediate) level, to the macro (large) level of musical structure.
At the micro-level, the smallest complete unit of musical structure, is a phrase which is comprised of patterns of material fashioned from the Eight Basic Elements. A phrase is a length of musical material existing in real time with a discernible beginning and ending. Phrases are usually eight to sixteen measures in length but may be longer. When relating musical phrases to melodic lines, it is important to realize that while melodies are comprised of complete phrases of patterned tones, each individual melodic phrase may be broken down into smaller incomplete units of melodic structure known as motives. Melodic motives are usually two- or four- measure patterns of melodic material. In sum, the micro level or musical structure is comprised of two units — the smaller and incomplete motive, and the larger and complete phrase.
The mid-level of musical structure is made up of sections of music. Phrases combine to form larger sections of musical structure. The length of a section may vary from sixteen to thirty-two measures in length - often, sections are much longer. Sections are punctuated by strong cadences. Longer songs and extended pieces of music are usually formed into two or more complete sections, while a shorter song or melody may be formed of phrases and have no sectional structure.
At the macro-level of musical structure exists the complete work formed of motives, phrases and sections. Both phrases and sections are concluded with cadences; however, the cadence material at the end of a section is stronger and more obvious in its punctuation.
These are the micro-, mid- and macro-levels of musical structure — motives, phrases and sections and the complete composition. This is the manner in which Western music is conceptualized as structure. Many other world musics are conceptualized in a similar manner. This approach of musical "mapping" may serve as an excellent "entry" to the unfolding of the architectural structure of any piece of music whether Western or non-Western.
Musical structure has a close affinity with architecture and mathematics. As a metaphor, music composition is often described as "architecture of sound" or "mathematics transformed into sound". Many compositional decisions that involve pitch relationships are mathematical in nature. Computer software programs - e.g., MatheMatica et al- now allow mathematic's equations to be transformed into sound.
Repetition of the material of music plays a very important role in the composing of music and somewhat more than in other artistic media. If one looks at the component motives of any melody, the successive repetition of the motives becomes apparent. A melody tends to "wander" without repetition of its rhythmic and pitch components and repetition gives "identity" to musical materials and ideas. Repetition is also used in chord progressions and in patterns of dynamics and timbre. Whole phrases and sections of music often repeat. The following illustration represents musical repetition.
a - a - a - a - a - a - a - a - a - a - a - a - a - a - a - etc.

Variation means change of material and may be slight or extensive. Variation is used to extend melodic, harmonic, dynamic and timbral material. Complete musical phrases are often varied; however, whole sections of music are usually not treated with variation. If one were to symbolize musical variation in a simple way using lower case letters of the alphabet, it would look like this:
a a1 a2 a3 a4 a5 a6 OR a a' a'' a''' a'''' a''''' a'''''' etc.