The 'classical' plan of movements included either three or four—the
latter number being the more common in quartets and symphonies. Of
these the first and the last were the longer and more essential. The first
is properly in 'sonata-form' and the last either in that or in 'rondo-form,'
and both are brisk in tempo, the last often a presto. The second, in slow
tempo, is either in 'song-form' or at least eminently lyrical, and the third,
if there are four, is properly a sprightly or even humorous minuet. The
keys of the first and last movements are the same, of course, but those
of the others may vary.
'Sonata-form' as a type of structure within a movement involves the familiar three divisions of exposition, development and recapitulation (see sec. 137), but, as understood in the 'classical' period, it also involves the principle that in the exposition there shall be either two distinct 'subjects,' the one in the tonic, the other in the dominant or (if the tonic is minor) in the relative major, or the same subject presented in the two keys successively. Haydn's practice was not consistent in requiring two different subjects. Ultimately the second subject was usually of a flowing, song-like character, contrasted with the more incisive and brilliant first subject. The 'exposition' tends to subdivide into parts—sometimes a brief introduction, then the first subject (often reiterated), leading to a transition into the contrasting key, in which is the second subject (also often reiterated), culminating in its key, often with a coda. For emphasis and clearness the whole exposition is regularly repeated. The 'development' is naturally the test of originality and musicianship. In it the materials presented in the subjects are freely handled, torn apart, combined anew, mixed with new material, interrupted by episodes or connective passages, and passed from key to key. Here the advance of the Haydn period over its predecessor was marked, since the need of definiteness and coherence was better felt, and the ways of working were better understood. The development properly ends in the contrasting key, but with an immediate and emphatic return to the original key, introducing the 'recapitulation' or 'reprise,' in which both subjects are restated, with a final climax and often a coda. Sonata-form is characteristic of the first movement, and hence is often called 'first-movement-form.' But it is also common in the last movement, and may occur even in the other movements.
The materials taken for 'subjects' from Haydn's time onward are almost always different in character from those used for contrapuntal treatment. Often they are distinctly lyrical, as if from a song, or solid harmonic progressions, as if from a part-song or chorale, or, if more distinctly instrumental, are employed rather for their pithy decoration of a metric pattern or a chord-sequence than for their adaptation to polyphonic unfolding. In a word, they are decidedly homophonic or harmonic in essence. And all the treatment given them is dominated by homophonic or harmonic principles. In details, of course, the part-writing must be careful and significant, and occasionally there are passages that recall the polyphony of the organ style, but in general there is some supreme melody or controlling harmonic progression that determines the form. Where exceptions occur, they are felt to be exceptions.
