Scarlatti has been called the founder of modern pianoforte technique. Although he composed for the harpsichord, he understood the instrument so thoroughly and what he wrote for it accords so well with its genius, that by unconscious anticipation it also was adapted to the genius of the modern pianoforte. It still is pianistic; more pianistic and more suitable to the modern repertoire than a good deal of music by greater men who lived considerably later. I should say, for example, that Scarlatti's name is found more frequently on pianoforte recital programs than Mozart's, although Mozart was incomparably the greater genius. But there is about Scarlatti's music such a quaint and primitive charm that one always listens to it with the zest of a discoverer, whereas Mozart's pianoforte music, although more modern, just misses being modern enough. This clever Italian gives us the early beginnings of the sonata form. He merely lisps in sonata accents, it is true, but his lisp is as fascinating as the ingenuous prattle of an attractive child. His best, known work, "The Cat's Fugue," the subject of which is said to have been suggested to him by a cat gliding over the keyboard, is indeed contrapuntal. But even this is a movement in a sonata, and the characteristic of his works as a whole is the fact that in most of them he developed and worked out a melody or theme, and that he established the fundamental outlines of the sonata form.
Comparatively few laymen have more than a vague idea of what is meant by sonata form. To them a sonata simply is a composition consisting of several movements, usually four, three of them of considerable length, with a shorter one (a minuet or scherzo) between the first and second or the second and fourth. A sonata, however, must have one of its movements (and generally it will be found to be the first) written in a certain form. Regarding the Scarlatti sonatas, suffice it to say here that with him the form still is in its primitive simplicity. For example, the true sonata movement as we now understand it employs two themes, the second contrasting with the first. As a rule, Scarlatti is content with one theme. It is the peculiar merit of Philipp Emanuel Bach that he introduced a second theme into his sonatas, or suggested it by striking modulations when he employed only one theme, and thus paved the way for its further elaboration by Joseph Haydn. Mozart elaborated the form still further, and then came Beethoven, with whom the classical period reached its climax and whose sonatas for all practical purposes have completely superseded those of his forerunners.