Final answer:
Bach's Brandenburg Concerto no. 2 follows the ritornello principle where a main theme presented by the full ensemble alternates with episodes featuring soloists, highlighting the evolution from modal to tonal music during the Baroque era.
Step-by-step explanation:
Bach's Brandenburg Concerto no. 2 in F Major is based on the ritornello principle, which means that a recurring thematic material (the ritornello) is presented by the full ensemble (the tutti), interspersed with episodes featuring individual soloists or smaller groups of instruments. This principle creates a structure where the main theme returns in different keys and combinations, serving as an anchor to the more freely developed solo sections. The ritornello form, typical in the Baroque era, is closely related to the development of tonality, as it often involves the modulation to different keys before returning back to the home key.
The use of the ritornello in the concerto introduces contrast and unity to the piece, as it interplays the soloist's virtuosic displays with the stability of the tutti, and drives the harmonic progression of the piece. Bach's use of this form reflects the evolving nature of music in his time, as the modal system of the Renaissance gave way to the tonal system of the Baroque, where the hierarchy of chords and the centrality of the home key became more pronounced. In essence, the Brandenburg Concerto showcases the Baroque fascination with elaborate musical forms and the burgeoning sense of musical architecture that would continue to develop into the Classical period.