In looking over the vast number of sonatas written between 1750 and 1800 one is impressed, if one is kindly, not so much by their careless structure and triviality as by their gaiety. In the adagios the composers sometimes doff their hats, somewhat perfunctorily, to the muse of tragedy; but for the most part their sonatas are light-hearted. They had a butterfly existence. They were born one day but to die the next. Yet there was a charm about them. The people of that day loved them. A run and a trill do, it is true, but tickle the ear; but that is, after all, a pleasant tickling. And simple harmonies may shirk often enough the weight of souls in tragic conflict, to bear which many would make the duty of music; yet their lucidity is something akin to sunlight. The frivolities of these countless sonatas are the frivolities of youth. There is no high seriousness in most of them. And our triplex form came sliding into music on a burst of youth. A star danced and it was born. What gave definite shape to this fundamentally simple form is the Italian love of melody. So far as it may be traced to the influence of one man, it may be traced to Giovanni Pergolesi, whose trio-sonatas first gave to the world as a prototype of the classical triplex form what is now known as the ‘singing allegro.’ Pergolesi was born in 1704 and lived to be only thirty-three years old; but in that brief life, gaily and recklessly squandered as it seems to have been, he exerted an influence upon the growth of music which apparently started it upon a new stage. He was all but worshipped by his countrymen. His opera, _La serva padrona_ (1733), won instant success, not only in Italy, but well over all Europe; and had an influence comparable to that of but few other single works in the history of music. On the ground of instrumental music his trio-sonatas have, as it seems now, accomplished scarcely less. We must here restrict ourselves to the harpsichord music of the time in Italy, in which the ‘singing allegro’ found place almost at once. Let us first consider what lay at the bottom of the new form.