It is not necessary here to inquire into the details of the part taken by Scarlatti in the erection of Italian opera as it now exists. His operas are truly epitomes of the history of musical development, and his many imitators and successors pass before us like the shadows of the Homeric shades; but we have only to do with him or with them in so far as concerns the main features of that form of operatic composition which Mozart found ready to hand.[11] The stability with which operatic development kept close to the path which had at first been marked out was due partly to circumstances and the influence of public opinion, partly to the character of the Italian people. Beauty, appealing immediately and directly to their lightly kindled imaginations, required that its sensual charm should be clearly and unreservedly expressed; and for this they were willing to sacrifice novelty and characterisation. Again, the art of music was developed in accordance with natural laws; and having once acquired forms indicative of its essential elements, it grasped these firmly, and refused to abandon them until they had become completely obsolete. It was the task of the great masters of the eighteenth century to {OPERA SERIA.} (160) maintain this course of steady imperceptible progress, and, by raising to successive stages each hardly won step towards perfection, to establish in the end a new and more admirable whole. The chief component parts of the opera were the recitative and the song, or aria.[12] Recitative, intended for the rendering of conversation, approaches in rhythm and intervals as near as possible to ordinary speech, and leaves the singer ample scope for an animated and expressive delivery. This is assisted by a simple harmonious accompaniment, the basses giving the fundamental, the clavier the harmony. The simplicity of the musical treatment lends itself to characteristic declamation, and impressive situations are thrown into relief generally by sudden changes of harmony; numerous instances show the importance that was attached to this mode of delivery. But very soon it became the fashion to treat this _recitativo secco_ as subordinate, and the composer strove to do away with it as far as possible. Certain turns, certain harmonic progressions and interrupted cadences, were as indispensable to recitative as many turns of speech are to social intercourse. As the course and development of the action of the piece depend almost entirely on the recitative, it follows that any neglect of the latter must affect one of the most important elements of the opera. The need for attaining the power of expressing a momentary passion or inspiration which would not admit of an elaborate representation led to the introduction of the so-called accompanied (obligate) recitative. For this the orchestra (at first only the whole body of stringed instruments) was made use of, and accompanied the alternations of emotion with corresponding musical phrases