Anyone that is interested in music should have at least a basic grounding in the principles of musical structure, whether they are a composer, a player or a listener.

Musical Ideas

Musical structure can be compared to writing out chapters in a story. Without structure, the music would leave the listener completely unsatisfied and the piece would merely be a random set of ideas. With a good structure, the music takes the listener on a musical journey, with a beginning, middle and end. This is why musical structure is one of the fundamentals of music.
To continue with the analogy of a piece of music being akin to a story, each piece must consist of hundreds of words. In music, these are called motives:

Motive or Motif

A motive must consist of at least two notes in order to have purpose and usually a motive will be made up of three, four, or more notes. In order to make up a line of music, a motive must lead somewhere and must link to the next motive and from the previous motive so that the piece flows well. By means of motive and its development, the composer conveys to the listener his musical idea and hence, the motives are the building blocks of the piece of music.

Phrase

A phrase is like a clause in a sentence, it consists of one or more motives and usually consists of a single idea, which is then repeated, complimented or added to by the next phrase.

Sentence

The natural length of musical sentence is eight bars. Some are shorter and some are longer, but (in the classical period especially) composers have tended to favour this length due to its symmetry and balance. Eight bar sentences consist of two halves made up of two phrases each, generally with the second half complementing the first. There are no rules, however, governing sentence construction so many different lengths and types of sentence can be found when listening to music.

Single Movement Forms

With many sentences of music, pieces take on a particular musical form. Musical forms vary from the simple to the very complex, from short pieces to long, and from thin textures to thick. Almost any piece written up until around 1920 can be said to have a distinct musical form and the majority of these will be explained in this section.

Binary Form

This is the simplest musical form that composers use and it consists of a question section and an answer section. These two sections, which we will call ‘I’ and ‘II’ are often repeated to make the differences between them stand out. To provide the question and answer (and to add interest), section I ends in a different key (usually the dominant) to the one in which it starts. Section II then goes through a series of modulations into different keys until it ends up at the home key once again.

Ternary Form

Ternary form is usually described using letters instead of numbers to show that the B section is contrasting. It is shown thus: ‘ABA’. Ternary form is quite simply an ‘A’ section, followed by a contrasting ‘B’ section and then the ‘A’ section repeated. Because of its simplicity, it is not often found in the works of the great composers, but is often seen in their longer solo vocal pieces – ‘arias’. It is then sometimes called ‘aria da capo’ form and at the end of B ‘da capo al fine’ will be written – meaning ‘repeat from the beginning until the word ‘fine’ (Italian for ‘end’) is reached.

Rondo Form

Rondo form is a progression of ternary form; it is a lot more commonplace than ternary form and is expressed as ‘ABACA’. The ‘A’ section is often itself in binary form and the ‘B’ and ‘C’ sections are deliberately contrasting.

Minuet¹ and Trio

This is another progression from ternary form. The two parts – minuet and trio – are in themselves ternary pieces. The structure here, is
‘A B A, C D C, A B A.’
Minuets often appear in classical music on their own, but in larger works such as sonatas or symphonies they are too short to comprise a movement in themselves. This is why the ‘trio’ is necessary. It sets itself apart from the minuet in that it is written principally for three instruments of the orchestra.

Variation Form

A piece that uses variation form begins with an initial theme, which is then extended and changed in various ways to create a longer piece. These variations can be continuous and move instantly from one to the other, or they can be separate, with each forming a particular movement of the piece.

Ground Bass or Basso Ostinato

The characteristics of a ground bass are similar to variation form but here, the variations are only in the higher instruments which are used to harmonise, compliment and decorate the repeating bass line. The ground bass was often used in particular by Purcell who also frequently wrote ‘chacones’ – triple time ground bass dances that pass the bass line from instrument to instrument to vary the texture of the piece.

Canon

The canon is a contrapuntal form ², which means a lot of emphasis is placed on the melody and its structure. In a canon, the instruments (often voices) play the same melody but at different times in relation to one another. (So one instrument will begin and another will start playing the same melody a few bars later). If the last few bars of the melody can be made to fit harmoniously with the first few bars then a loop can be created. This would be called a ‘round’. A well known example of this is ‘Frére Jacques’.

Fugue

Many musicologists do not consider the fugue to be a musical form at all because fugues are so variable in their structure. Nevertheless, fugue is an important style and a recognisable one and can be considered to be a form for the purpose of study.

The fugue is another contrapuntal form, similar to the canon but more complex. It involves the overlapping of several melodies, beginning with an initial theme or ‘subject’. This subject is developed and repeated or developed becoming a counter-subject, at which point another instrument may enter and play the ‘answer’ - an imitation of the subject, often transposed into the dominant key so that the parts sound different, yet stay in close harmonic relation.

Subsequent overlapping parts may engage in ‘free-counterpoint’ with the other instruments. This is a tune that is mostly unrelated to the subject and answer, yet fits well with the other parts.
Other fugal techniques include the ‘codetta’ – a linking section between parts and the ‘episode’ – often a thematic development from the subject, this serves as a relaxation or transition between parts.
As these parts overlap and interlock amongst one another, the piece takes shape. The conventional structure of a fugue uses three sections: the exposition, the middle section and the final section.

The exposition serves as an introduction to the various parts, with each instrument or voice playing the subject once or more. The parts are staggered in their introduction, interlocking and modulating between the home and dominant keys.

The middle section compliments the exposition by introducing episodes, imitations and various modulations to add variety and interest. Also common in the middle section is the use of long rests in certain parts to vary the texture of the piece .

The final section takes development further and comes to a climax at which the piece is rounded off. Often in the final section, the subject is changed in a particular way. This is usually by augmentation ³, diminution ⁴ or inversion ⁵. Usually the piece is rounded off with a Coda.

Sonata Form

Sonata form should not be confused with the sonata. A sonata consists of many movements whereas sonata form describes the structure of a particular movement or piece. Sonata form is usually used in movements of sonatas, symphonies and concertos. It is also occasionally used in single movement works, such as the overture.

A piece or movement in sonata form consists of three parts. These parts are more complex than in the other simpler forms, they are: the exposition, the development and the recapitulation.

The Exposition

This is where the main themes are introduced. There will be many familiar lines that appear throughout the piece but overall there are two main subjects that are put forward. The first subject is usually rhythmical and bold; it is sometimes referred to as having a masculine character. This then leads to a transition section which uses material from the first subject and transposes into the key of the second subject, which is generally the dominant, or the relative major or minor of the home key. The second subject is usually more feminine in character, being more melodious and lyrical. When this is over the section ends in a codetta ⁶ and leads straight into the development.

The Development

The material from the exposition is developed to a climax. Here the composer will use a variety of techniques and different keys to create interest; occasionally he will write new material for the development as well. Throughout the development, the tension builds steadily until the eventual culmination of the two subjects.

The Recapitulation:

The tension is relieved by appearing to repeat the exposition. However, the familiar subjects and motives of the beginning of the piece have undergone slight changes or modifications to create further interest. The second subject is now in the tonic or ‘home’ key and the composer will have altered many of the ideas of the exposition. It is as if the conflict in the development section has caused ripples of unfamiliarity in the recapitulation. The piece ends with the codetta from the exposition – now in the tonic key.

Sonata Rondo

This is a combination of sonata form and rondo form. Often it can be found in the last movement of a sonata. The structure still comprises of the exposition, the development and the recapitulation but now the exposition and recapitulation sections are in ternary form so the piece looks like this:
‘A B A C A B A’.

Here, the ‘A’ is the first subject, the ‘B’ is the second subject and the ‘C’ is another episode, usually containing development.

The Overture

The overture is written to introduce an opera or an oratorio. Overtures can be categorised thus: the French Overture, the Italian Overture and the Concert Overture.

The French Overture consists of two sections – slow and quick. The first is grand, sombre and usually contains dotted rhythms as a main idea. The second is light and almost scherzo ⁷ in its mood.

The Italian Overture eclipsed the French Overture in the eighteenth century. It was briefer, yet consisted of three sections – quick, slow, quick.

The Concert Overture does not introduce an opera; it is an independent work. It is usually in a kind of sonata form, but the rules governing sonata form are not taken so literally. Often these overtures are based on a story.

It is also important to note that as many overtures are of a very high musical standard, they are often played on their own – as concert overtures. Although they were originally intended to introduce an opera, we often hear them at concerts because the operas for which they were written for are too long.

Multi-Movement Forms

The Sonata

A sonata is a multi-movement piece for one or two movements with at least one movement in sonata form. There is no set number of movements for a sonata but generally it is made up of two to four, most frequently four movements.
The most common structure of a sonata is:

First movement: Sonata form

Second movement: Ternary form ⁸

Third movement: Minuet and Trio

Fourth movement: Rondo ⁹.

This is a usual layout for a sonata; however, the structure of a sonata varies from composer to composer and has no strict rules governing the forms of the movements.
The tempi of the movements are usually composed thus: (1) Fast, (2) Slow, (3) Moderate, (4) Fast. This creates a pleasing balance between fast and slow movements. When three movements are used, the structure is generally: (1) Fast, (2) Slow, (3) Fast.

When more than two instruments are used, the piece ceases to be a sonata and becomes a trio (for three instruments), quartet (four), quintet (five), sextet, septet etc. A sonata for full orchestra is called a ‘symphony’.

The Concerto

A concerto is a piece for solo instrument accompanied by a full orchestra, it usually follows the same plan as a sonata, though various composers use this in different ways. Whereas Mozart left the soloist out for the entire exposition, Beethoven and many later composers did not follow this practice.
A concerto written for two instruments is a ‘double concerto’. (A three instrument concerto is a ‘triple concerto’ and so on).

When a small group of instruments ¹⁰ is accompanied by a full orchestra ¹¹ this is called a ‘ Concerto Grosso’. The concerto grosso is mainly a baroque form, the chief composers being Corelli, Vivaldi, Bach and Handel. A concerto grosso usually uses a harpsichord as well as the baroque orchestra.

The Suite

A suite is a collection of dances to be performed one after the other. During the seventeenth and eighteenth centuries this was one of the most popular and important forms. The main four dances that appear in a suite are: the Allemande, the Courante, the Sarabande and the Gigue. Other dances that may appear in a suite include: the Minuet (which is mentioned later), the Gavotte, the Bourée, the Musette and the Passacagalia.

The Allemande

This is a dance in simple quadruple time (4/4 time) at a moderate pace. It usually contains semi-quaver scales, often with an upbeat.

The Courante

A courante can be categorised as either a French or an Italian courante. A French courante is in compound triple time (3/2 or 6/4) and contrapuntal, containing various polyrhythms.
The Italian courante is a lively and in simple triple time (3/4) instead of compound triple time.

The Sarabande

This is a Spanish dance in a slow triple time such as 3/2 or 3/4. It has an accent on the second beat and is more harmonic than the other dances.

The Gigue or Jig

This is the finale of the suite. It is fast and exciting and imitative – sometimes fugal. Generally speaking, it is in compound triple time (3/8, 6/4, 9/8 or 12/8).