The word Pastoral is derived from the Latin adjective pastoralis ("appertaining to shepherds") and can be discerned as a form of literature as far back as Hesiod in the 7th century B.C., In music, as in literature, it is seen as having to do with country life and rural themes. As a musical term (often seen in the French “Pastorelle” or French and Italian “Pastorale”), it came into Western music through certain songs of the troubadours and trouvères in southern and northern France respectively in the 11th and 12th centuries.
The earliest piece of English lyric verse to which we have a tune is the pastoral “Sumer is acumen in” from about the 1240s. Also about this time a play on the frivolities of “Robin et Marion” was set to music.
Many songs of the 15th century – French chansons Italian frottola and early madrigals – concerned themselves with love in the open air and the pleasures and vicissitudes of rural life. This continued into the 20th century with Joseph Canteloube’s extremely popular and oft recorded collection of folk songs, '“Chants D’Auvergne”.
The theme of the amorous shepherd, of nymphs cavorting with shepherdesses in Arcadian glades and fields was a favourite theme in early operas and at the courts of England and France into the eighteenth century. The late 15th century Venetian play “Il pastor fido” (“The Faithful Shepherd”) was given many musical treatments including one by Handel as late as 1736.
As a term descriptive of the music rather than the subject, the term gained currency during the 18th century to describe music that sounded like a country dance. This was music with a ground bass suggestive of bagpipes (a particularly rustic instrument once pried away from the Scots) accompanying country dance-like rhythms. J. S. Bach wrote a “Pastoral Symphony” into his “Christmas Oratorio” as did Handel into “The Messiah”
Major pieces with the term attached (either by the composer or others) include symphonies by Beethoven, Vaughan Williams and Alexander Glazunov, a piano sonata by Beethoven, Joaquín Rodrigo’s “Concierto Pastoral” (flute) and various suites, fantasias and other descriptive pieces. Emmanuel Chabrier’s orchestral “Suite Pastorale” is especially popular.
“The Grove Concise Dictionary of Music”
“Oxford Companion to Music”