The Baroque era established the tonal harmonic system, invented the modern orchestra, perfected the opera, and produced J.S. Bach - whose counterpoint represents the summit of 400 years of polyphonic development.
The Baroque era, spanning approximately 1600 to 1750, is the period during which Western music established the tonal system that would govern virtually all subsequent European and American music for the next three centuries. Tonality — the organization of musical pitches around a hierarchical relationship between a central key note (the tonic) and the other pitches of the scale, with particular weight given to the relationship between the tonic and the dominant (a fifth above it) — was not invented at a single moment but emerged gradually from the late Renaissance practice of polyphony as composers and theorists worked out the harmonic implications of the major and minor scales. By the early seventeenth century the system was sufficiently established that composers could exploit the expectations it created — the sense of tension when music moves away from the tonic key, the sense of resolution when it returns — as a primary structural resource. The Baroque era saw this resource exploited with increasing sophistication, culminating in the work of Johann Sebastian Bach, whose music is simultaneously the synthesis and the summit of everything the period achieved.
The new musical forms and genres that the Baroque invented or codified defined the landscape of Western concert music through the nineteenth century. The concerto — a work for solo instrument or small group of soloists in dialogue with a larger orchestra — was established by Arcangelo Corelli (1653-1713) in the form of the concerto grosso, in which a small ensemble (the concertino) is set against the full orchestra (the ripieno). Antonio Vivaldi (1678-1741), working in Venice at the Ospedale della Pieta — a home for illegitimate and orphaned girls, many of them trained to a high musical standard — composed more than 500 concertos that established a three-movement fast-slow-fast structure, a convention of instrumental dialogue, and a melodic vividness that influenced every subsequent concerto composer, including Bach, who transcribed several of Vivaldi's works for keyboard. The Baroque also developed the oratorio — a large-scale work for soloists, chorus, and orchestra on a religious or dramatic subject, performed without staging — largely in the hands of George Frideric Handel (1685-1759), whose Messiah (1741) remains the most frequently performed choral work in Western history and whose Italian operas for London audiences demonstrated a command of vocal writing that made him the dominant musical figure in England for three decades.
Opera during the Baroque moved from Monteverdi's foundational experiments through the elaboration of the da capo aria — a three-part song form (A-B-A) in which the return of the opening section gave the singer an opportunity for elaborate improvised ornamentation — into the highly stylized form known as opera seria, which governed the genre through the early eighteenth century. Opera seria organized plots around heroic and mythological subjects, divided the musical content strictly between recitative (for narrative) and aria (for emotional reflection), and placed the greatest vocal demands on the castrato singers whose extraordinary range and power made them the superstars of Baroque musical culture. Handel's 42 operas, most of them written for London, were composed within these conventions while frequently transcending them through the depth and variety of his characterization. The keyboard suites, orchestral water music, and concerto grossi he produced alongside the operas demonstrate the Baroque's characteristic tendency toward multi-movement collections organized around dance forms — the allemande, courante, sarabande, and gigue that constituted the Baroque suite.
Johann Sebastian Bach (1685-1750), working throughout his career in modest German positions as organist and kapellmeister — in Arnstadt, Mühlhausen, Weimar, Köthen, and finally Leipzig, where he spent the last twenty-seven years of his life as Director of Music — produced a body of work that achieved a synthesis of the entire Baroque tradition at a level of technical mastery and expressive depth that his contemporaries recognized as extraordinary but that subsequent generations have increasingly understood as the most comprehensive achievement in Western musical history. The Well-Tempered Clavier (two volumes, 1722 and 1742) demonstrated well temperament — a tuning system that distributes the small mathematical compromises of the tonal system across all keys, making all twenty-four major and minor keys usable, each with its own colour — by providing a prelude and fugue in each key. The Goldberg Variations (1741) took a simple bass line and harmonization and generated thirty variations of extraordinary structural and expressive variety, each double bar repeated, the whole framed by an opening aria whose return at the end transforms the familiar theme into something touched by the music heard between. The six Brandenburg Concertos, the Mass in B minor, the St. Matthew Passion, the forty-eight fugues of the Well-Tempered Clavier, the cello suites, the violin partitas — collectively they document a musical intelligence that has never been surpassed in any subsequent period. After Bach's death in 1750, his music was largely unknown outside a circle of specialists; Felix Mendelssohn's revival of the St. Matthew Passion in Berlin in 1829 initiated a rediscovery that has accelerated ever since. Bach is today the most recorded and performed composer in Western history. His influence on subsequent composers has been extraordinary in its breadth: Mozart studied his contrapuntal technique late in his life and his last works show the influence; Beethoven learned the Well-Tempered Clavier as a child and quoted Bach's harmonic language at critical structural moments throughout his career; Brahms edited and published Bach editions as a scholarly act of homage; Shostakovich wrote his own set of twenty-four preludes and fugues in 1950-51 in explicit dialogue with the Well-Tempered Clavier. The jazz pianist Keith Jarrett has recorded the Well-Tempered Clavier complete; the guitarist Andrés Segovia transcribed the lute suites; Wendy Carlos synthesized the Brandenburg Concertos on Moog synthesizer. Bach's music has proven remarkably adaptable to performance contexts its composer never imagined, suggesting that the structures he created have a quality of inherent rightness that transcends the specific sounds of any particular instrument or performance tradition.