Concerto
The term "concerto" is given different meanings depending on historical context; up to the early 18th century it was basically "a diverse ensemble of voices, instruments, or both, or a composition for such an ensemble;" as early as late 17th century it could be used to describe "a multimovement (occasionally multisectional) work for soloist or soloists and orchestra." Early on there was some kind of textural or instrumental differ-entiation between the "solo" and the larger group, but not uniformly defined. The term initially described sacred works; secular pieces adopted other, more specific names.
By the Baroque period three broad types of concerto developed: the concerto grosso, the ripieno concerto, and the solo concerto. The concerto grosso consisted of a small instrumental (concertino) ensemble against an orchestra (usually a string orchestra plus continuo, the concerto grosso). The concerto grosso "arrived" to a standard form with Alessandro Stradella in the 1670s. Eventually, however, the form would change, even apparently abandon the formula Stradella had established, due in large part to the works of Arcangello Corelli, who "made frequent use of what has been called the concerto style, an all-important Baroque style featuring idiomatic string figuration, ... clearly directional harmony, ... motoristic rhythm, and relatively homophonic texture." Torelli and Vivaldi would further alter the form to become "less a concerto grosso than a concerto for two individual soloists."
The ripieno concerto came later, a piece that varies from the concerto grosso in that there is no soloist (or at least "subsidiary ones"). They tend to be either sonata types, "four-movement slow-fast-slow-fast cycles and predominantly fugal [in] textures;" or sinfonia type, a "three-movement (fast-slow-fast) pattern and more homophonic texture familiar to us from the solo concerto and opera sinfonia." It was this form of concerto, around 1720, that began the "tutti-solo" practice.
The solo concerto (for solo instrument, usually violin, and orchestra), followed a three-movement cycle in ritornello form, with clear solo episodes interspersed among the orchestral ritornellos. The primary Baroque composer of solo concerto was Antonio Vivaldi, who "firmly [established] the three-movement cycle as the norm." The form was extremely flexible, however; in many of his concertos, the middle section contains brief and numerous alternations between solo and orchestra, rather than the formulaic "ripieno-solo-ripieno-solo-ripieno-solo-ripieno (maybe additional solo-ripieno)."
"Concertos for instruments other than violin began to appear in the 18th century." Handel contributed to early organ concertos; Bach some for harpsichord. In the Classical period the solo concerto firmly established itself as the dominant form, and "witnessed the coming of age of the keyboard concerto," specifically for piano (rather than the antiquated harpsichord). Most Classical concertos are composed of three movements, following what seems to be an extended sonata form. "Mozart's 23 original piano concertos...represent the crowning achievement of the 18th century."
Beethoven's treatment of the concerto became the model that subsequent Romantic composers would follow. Mendelssohn made his contribution of the formal type for the first movement, though some composers still used Beethoven's procedure. Mendelssohn also removed breaks from the movements.
The 19th century saw a focus on composition for virtuoso playing, still primarily for violin or piano. "Movement structure in most of these works is patterned on the by-now conventional ritornello-sonata type perfected by Mozart and Beethoven." The 20th century "basically continued the 19th-century concept of the concerto (and often its forms and styles)," even among the "atonalists." The composers of the neoclassical movement, however, went back to the pre-Romantic forms. In Stravinsky's Violin Concerto "the soloist is treated more as a member of the ensemble than as a virtuoso protagonist," and "the solo concertos of Paul Hindemith...are more traditional than the foregoing works in their treatment of the relationship between soloist and orchestra." There was also the influence of jazz on the form (Copland, Gershwin, and Stravinsky, just to name a few contributors), and the "concerto for orchestra," where the orchestra itself functions as the virtuoso rather than in ripieno style.
Concerto grosso
"A concerto for a small group of soloists (the concertino) and orchestra (the tutti or ripieno)."
White, John D. "Normative Structures." The Analysis of Music.
White frames the subject by warning that the definitions and expectations of form-labeling, while generally consistent, will in any specific form represent only a minority of pieces. "Examples of deviations from these norms," he says, "are more common than the norms themselves in the actual literature of music." The patterns in discussion are more significant than the terms used to describe them.
Binary form, or full binary form, consists of two sections with at least three phrases. In 17th- and 18th-century pieces the repeat sign is a consistent feature, but not necessarily expected to be observed (apparently serves as much as a "place mark" as a marking to be followed). The Baroque binary, with its constant movement, differs from the Classical style, with "clearly delineated phrases [and] clear-cut cadences." An extension, the rounded-binary form, involves "the restatement of the opening thematic material in its original key in the middle or shortly before the end of the second section," and "is an important step in the evolution of sonata form."
In the three-part forms, the idea a discreet musical idea at the beginning and end, with a different idea in the middle, "contrast is achieved by means of harmony, rhythm, motivic development, or texture, rather than by the presentation of entirely new melodic material." White says it is probably safer to say that such a ternary form should only be named such if the middle section is of sufficient length and thematic material.
Rondo form, a natural progression from the ternary, involves adding sections of music in different (but usually predictable) tonalities, almost always divided and capped by a consistent rondo theme in the tonic key. A Classical rondo "a characteristic rondo theme was a well-rounded entity in itself--very often a double-period or a short binary or three-part form invariably ending with a perfect authentic cadence on the tonic." Episodes, the sections separating the rondo theme sections, "add contrast to rondo movements--harmonic contrast by shifting to related keys or change of mode, melodic and rhythmic contrast by use of new thematic material, and contrast in sound by changed instrumentation, texture, or dynamics. Unlike the rondo theme, episodes usually are not harmonically closed and are often rather developmental in character."
The sonata form involves the exposition of musical themes, moving "from the tonic to the dominant (or some substitue for V such as III in minor), and then, through various more or less stylized tonal excursions [development[, back to tonic" for a recapitulation of the first material. It is clearly an extension of the Baroque rounded binary piece; the main difference is that it tends to make user of longer exposition and recapitulation sections. It also involves a second tonal group in the exposition, a tonally-unstable period where the first group's themes are developed, and a "literal return of the main theme in the key of the tonic." "Sonata form was the most important single movement instrumental form throughout the Classical and Romantic periods and continued to be used, though very freely, even in the twentieth century." It invariable involves at least two "contrasting tonal areas or groups in which thematic material is presented;" a development which makes use of a period dominant preparation preceding the recapitulation; and may contain a coda of substantial length.
The sonata-rondo is, basically, a piece in basic sonata form, due primarily to key relations and the use of material from B in the C section (or instead of it). It "occurs almost nowhere except as the last movement of three- and four-movement works of the late 18th- and early 19th-centuries (a few in [the 20th century])."
Concerto patterns involved the concerto grosso, a small group (concertino) playing against a larger group (ripieno); the orchestral concerto, similar to the concerto grosso but dispenses with the contrasting groups of instruments; and the solo concerto, with a solo instrument against a ripieno. After Torelli, "all three types usually followed a three-movement pattern of a fast movement, a slow movement, and a fast final movement." It differs from a rondo in that ritornello sections may be in different keys rather than the tonic (which it uses usually just at the beginning and end of the work).
"Variation is the process of changing or modifying a musical passage in such a way that the result is recognizable as having been derived from another passage, often retaining the length and general contour of the original." It varies from development in that it is more concerned with retaining the "identity of the musical idea" than exploring the harmonic and tonal possibilities of an idea. It generally applies to a complete musical idea rather than a short motive. It was used early on as a decorative technique to "embellish the theme with new figurations" for secular songs and dances. Later on the technique was applied to sacred music, and ultimately the ostinato variation, which includes the passacagtlia style (which typically involves variations on the bass line) and chaconne style (which usually only deals with the harmony).
The classical theme and variations is next, involving a complete, harmonically closed theme, with variations following in almost exactly the same harmonic patterns. The character variation of the 19th century involves profound alteration among the separate variations of the character of the theme. Basso-ostinato variations, which "springs from the Baroque ostinato variation," differs in its less homogeneous texture, and unique contrapuntal style. The free variation involves the abandonment of the "structure and harmonic patterns of the theme in favor of free development of motives from the theme."
Contrapuntal works include the fugue, a highly-organized style of imitative piece; the strict canon, which employs strict imitation among two or more voices throughout the piece (a free canon departs from imitation at some point); and the ricercar, ancestor to the fugue.
Rondo
The word "rondo" has two primary meanings: the first (and less used) pertains to a late-18th-century aria with a slow first section and fast second, both of which are usually repeated, but in this usage the word is usually spelled rondo; the second and more common usage pertains to "a multisectional form, movement, or composition based on the principle of multiple recurrence of a theme or section in the tonic key."
The rondo itself consists of a principle theme or section, usually represented by the letter A--the "refrain" or "rondo theme." This theme alternates with other sections called couplets or episodes, which are sequentially labeled B, C, etc. Typically the rondo theme is set in the tonic key (unlike the ritornello, which may present the principle theme in any number of keys) and is a rounded binary form. Common designs are the two-couplet ABACA type, the serial ABACADA ("also characteristic of the rondeau as well as of early Classical rondos"), the "symmetrical or arched" ABACABA, and abbreviated versions like ABACBA.
The rondo is a Classical version of the French Baroque rondeau, and the shift to the newer form probably was caused by the Italian opera buffa. "Independent rondos, sometimes with slow introductions, were fairly common during the Classical period." It was usually used "as one movement in a larger work, in which function it provided the principal alternative to sonata and related forms."
The sonata-rondo form is "a mixed form incorporating the sonata and rondo principles in varying degrees." It is can often be broken down to ABACAB'A, where the ABA and AB'A sections function as exposition and recapitulation (where the B is frequently in the dominant or mediant key, and B' is in the tonic), with a developmental C section. However, "no single scheme can account for the many variants." They appeared as early as 1768 in London, an important center of rondo composition.