The most striking aspect of this little piece is the obvious, clear divisions of the sections. The first section is marked off from the second by the double bar for the repeat. There is a pause before the third section, or restatement, begins. But clearest of all is the arrangement of musical material. By this we know positively that the triplex form has become firmly fixed, that the old binary form has expanded to a ternary form, submitting to the same influences that had made the perfect aria and the perfect fugue. It will be remembered that in the old binary form, composers made little effort to differentiate the material proper to the dominant part of the first section from that which had already been given out in the tonic. Such pieces dealt not in clear themes but in one or two running figures which lent themselves to more or less contrapuntal treatment. The opening figure was usually the most definite. The second section began with this figure in the dominant key; but in the final restoration of the tonic key the figure played no part. In other words, the chief figure of the whole piece almost never appeared in the second section in the tonic. It was not until the embryonic middle section, which, as we have seen, consisted of but one or two modulations, had developed to something of the proportions of the contrasting section of the aria, that composers realized that in order fully to re-establish the tonic key at the end, the chief figure should again make its appearance and usher in the final section, which thus became a restatement of the first. Scarlatti’s treatment of the binary form was always brilliant and clear. He was, as we know, fertile in sparkling figures. His sonatas are always made up of two or more of these, which, unlike the figures in the suites of most of his contemporaries, are distinct from each other. But in most of his pieces, long as the middle section might be, the tonic key was never re-introduced by the return of the opening figure of the first section. It is precisely this that he has done in the sonata in C major now in question. The first section presents two distinct figures or subjects, one in the tonic, the other in the dominant. The first, or opening figure, is in the nature of a trumpet call. The second is conspicuous by the wide crossing of the hands. The second section begins immediately after the double bar in the proper manner of the binary form; that is, with a modification of the first subject in the key of the dominant. Then follow many interesting modulations, leading to the unmistakable half-close, prefatory to the third section. And the third section begins at once with the _first_ figure in the _tonic_ key, and proceeds to the second, now likewise in the tonic. This, more than all else, marks the passing of the binary form into the triplex. The Padre Martini adagio presents the same feature, but less clearly because the second figure is hardly articulate.