Haydn has been called the father of the symphony and the string quartet, and his most important compositions are in these departments. But a symphony is simply a sonata for orchestra, and a quartet is one for four instruments. Hence we shall find that Haydn's piano sonatas show the same advances in form as his symphonies and quartets. In the first movements of three of his earliest sonatas (op. 22, 24, and 29) he uses in the propositional part two principal themes, wholly different from one another. He did not, however, in the works of his middle life follow this plan, but in his English symphonies he used second themes invariably and in a manner which allows no room for doubt as to his definite purpose. The form of his first movements is clear and symmetrical. It is in three parts, the proposition, discussion, and conclusion being plainly distinguished. The working out part is shorter and simpler than those found in later sonatas, such as Beethoven's. But Haydn's first movements convince the hearer of their claims to consideration as works of art on lines of design carefully planned. The systematic use of the second theme was adopted by all subsequent composers, and was the means of raising the sonata from an experiment to the most satisfactory and convincing of all musical forms. In Haydn's three-movement sonatas the appeal to the intelligence by the opening allegro is always followed by an appeal to the emotions in a slow movement, with broad melody and harmony and much sentiment. His finales are always bright and lively, and frequently sparkle with gayety. In form the finale is usually a rondo, an early cyclical form in which a single melodic subject is periodically repeated, the repetitions being separated by passages of new matter. When Haydn wrote a sonata in four movements, he introduced as the third the minuet, a piece of music in dance rhythm. Emmanuel Bach had used this form in one or two of his sonatas, but it is easy to see that the idea was originally suggested by the alternation of different kinds of dances in the archaic sonatas of Biber and Corelli. The minuet, being a graceful and elegant dance in triple rhythm, formed a most excellent bridge between an emotional slow movement and a jocund finale. The minuet movement consists, as a rule, of two parts, called minuet and trio. In the old dance it was customary to give relief to the first melody by a second, always written in three-part harmony and hence called "trio." This plan, except the adherence to three-part harmony, was followed by the artistic composers when they adopted the minuet as part of the sonata. In addition to what has been said, two important facts must be noted. Haydn was intimately acquainted with the simple, fluent melody of Italian music, and he was not acquainted with Bach's "Well-Tempered Clavichord." The result was that his themes are all essentially song-like in character. They are more extended and more definite in shape than Emmanuel Bach's, and they