From the very beginning opera brought together all the arts. It involved painting, poetry, drama, dance and music, making it the most complex of art forms. It was, as Samuel Johnson later pointed out, exotic and irrational, and, as many have found, remarkably expensive. It remained, nevertheless, of continuing social and political importance. In the first respect it edified and entertained, and in the second it served as an expression of the power and splendour of the monarch in an age of kings.
Early opera had involved madrigals, dramatic monody and set songs, or a mixture of these. As the 17 th century went on, there developed a gradual distinction between recitative and aria. The first of these, lightly accompanied often simply by chords, follows the rhythm and stresses of speech without the formal structure of a melody. Recitative, in fact, is dialogue set to music. The aria is a song, often in a form that frames a middle section in identical outer sections, the second of which might be ornamented by the singer. While the plot may be carried forward by the recitative, the aria tends to embody one state of mind. Both had an important part to play in what followed, although audiences tended to pay more attention to arias and much less to recitative, which seemed tedious.
The later years of the 17th century brought the beginnings of operatic reform. This came about partly as a result of French criticism, based on the Aristotelian principles that dominated French classical tragedy. There the so- called dramatic unities of time, place and plot were to be observed. These demanded a closer connection between time in the drama and time on stage, some limit on the changes of place possible, since in Greek tragedy no change of scene was allowed, and a final unity of plot, without primitive diversion into unconnected sub- plots. Under the leadership of the librettist Apostolo Zeno in Venice, the art was purged of its comic elements. The new form, later known as opera seria , followed clear principles of classical propriety and led to a certain stylization. There were clear categories of major and minor r๒les, usually for six or seven solo singers, and of the number and type of arias to be allocated to each. Subjects tended now to be historical, rather than mythological. Opera seria held a central position in repertoire for three- quarters of the 18 th century. It brought the rise to prominence of the castrato , now cast in the principal male r๒les, and allowed a similar importance and scale of fees to the prima donna , the first lady. Each would expect a similar number of arias of varied mood, sad, angry, brave or meditative, irrespective of the demands of the plot, while the secondary singers would have their own demands to make.
After Zeno the principal librettist was Metastasio, regarded as the most outstanding dramatist and poet of his time. The new libretti, the operatic texts, were set again and again by major composers of the day, including Vivaldi. The music, in fact, became relatively expendable. It was often a case of first the words, then the music. In London Handel had opera seria libretti adapted for the varied requirements of London audiences. He was followed in London, later in the century, by another German composer, Johann Christian Bach, the youngest son of old Johann Sebastian, but the art remained essentially an Italian one.
In the 18th century there was a parallel development of what was later known as opera buffa (comic opera). This had its roots in the ancient Roman comedy of Plautus and Terence and this in turn had been derived from ancient Greek New Comedy. Features of these were stock characters, comic and cunning servants, angry and parsimonious fathers, passionate lovers, amorous daughters and bragging soldiers. With them came a preoccupation with what was recognisable as ordinary life, however simplified. Another source of Italian comedy was found in the associated improvised theatre of the commedia dell'arte , with its similar array of stock characters. Opera buffa corresponded to contemporary spoken drama and opera texts owed a great deal to the work of the playwright Goldoni. Oddly enough, the earlier historical process was now reversed. In the 17 th century tragedy had acquired comic elements. Now serious characters began to find a place in comic opera, which became less comic and more realistic. These more dramatically credible plots found a place in Italian operas such as those written in Vienna by Mozart and his librettist Lorenzo da Ponte and their contemporaries.
Serious Italian opera, again at first in Vienna, underwent a marked reform with the work of Gluck and the librettist Calzabigi. Between them they succeeded, largely under French influence, in introducing simplifications. The formal requirements of the old opera seria were reduced, allowing a greater degree of realism. Gluck, in fact, claimed that he made music the servant of poetry, never introducing novelties or distractions from the dramatic situation. He explained his principles clearly in his introduction to the opera Alceste, published in 1768. These had already been put into practice in 1762 with his version of the story of Orpheus, Orfeo ed Euridice (Orpheus and Eurydice).