Between Sonata- and Rondo-Form: A New Hybrid Musical Form from Boccherini's Last Works in the Background of the Viennese-Classical Period
At the end of Boccherini's composing period, numerous fast movements from his chamber repertoire - apparently written in a sonata-form -, contain a repetition that is atypical for the normative scheme of the sonata-form.
A repetition of the developing section (entirely, but sometimes partially) is placed just after the repetition of the first part (exposition), before the second part continues with the re-exposition – or reprise – and codas (which are not repeated).
As far as I am aware such a scheme is strictly confined to Boccherini, but it should not be considered as an anomaly. It is rather the consequent outcome of two different formal/linguistic factors, that largely influenced the instrumental music by and regarding Boccherini.
The first of these two factors consists in the appearance of new hybrid forms in the last half of the 18th century instrumental music, like the "variation-rondo" (a form found prevalent in Haydn’s own music, viewed also as "double variation"), and well-known "rondo-sonata". Mainly developed in the Viennese-classical milieu, the rondo-sonata combines some building principles from rondo (alternation of a refrain with one or more strophes; short connections between the strophe and the following occurrence of the refrain; an internal symmetric structure for the refrain) with some structural principles of the sonata-form. In the rondo-sonata (a conclusive movement), the formal frame is the same as a 7-section rondo (4 refrains - one or two of them can be omitted- alternated with 3 strophes), but some elements - if coherent with the rondo scheme - are taken from the sonata-form: the whole tonal disposition (first strophe occurs at the dominant, then at the tonic); a second strophe (fourth section of rondo) that functions - thematically and structurally - as an authentic development, etc.
In Boccherini’s case, (he who very rarely employed - and as an initial movement - a normal rondo-sonata), the process to build the form is inverted: the whole frame is the same than one of a sonata-form, and some elements are bound with the formative logic of the classical rondo: The repetition of the development, carried out as if it were an independent rondo-section; the characteristic tonal connection before re-occurrences of the refrain (a connection, modulating toward the tonic, is very common at the end of the exposition); the presence of a final strophe, which can be considered a sonata-form Coda as well as the last occurrence of a rondo refrain.
It is for this reason that I would call this hybrid formula a "sonata-rondo", in order to distinguish it from the Viennese-classical rondo-sonata and also to underline the pivotal role of the sonata-form scheme and its prevalent position within an entire Sonata, without however considering it as a rigid scheme: it's rather a variable result of a group of formative elements that can be used freely, even individually, but that can also operate together organically. These can be identified at a more profound level, in the musical language of Boccherini, as the second formal-linguistic factor: The personal tendency towards an iterative and sequential logic, although proportioned with the directional form and thematic working of the classic sonata-form.
Such an issue will be illustrated with some specific examples from Quintets op. 55, 56 and 57 and String Quartets op. 58, as well as two-viola Quintets op. 60 an 62.