But we need look no further than Beethoven if we wish to see this principle in its most perfect embodiment. The opening movements of the two Sonatas, which he has numbered as Op. 27, stand on the outside verge of organic style: the former contains the maximum of diversity without being indefinite; the latter the maximum of unity without being monotonous: and between their bounds lie all those marvellous examples of contrast and antithesis, of variation and development, of firm outline and steadfast plan, which have placed his work as far beyond rivalry as that of Angelo or Shakespear. See how the stormy opening of the Waldstein is soothed and quieted by the melody of the second subject: how the bleak majesty of the first theme in the Appassionata finds its complement in the warm, rich tune that enters upon the change of key. Look at the balance of phrase in the first Rasoumoffsky Quartett, in the fifth Symphony, in the Emperor Concerto. But indeed the fact is too patent to need illustration, even if the selection of instances were possible. One might as well try to pick out examples of Milton's dignity and Goethe's wisdom, or direct attention to evidences of skill in Titian and Velasquez. Even the few imperfections may readily be condoned. The finale of the first Sonata is a legacy from an alien system: that of the Eroica an obvious experiment, that of the Sonata in A major an instance of the curious devotion to counterpoint which Beethoven specially manifested at the end of his career. And it should be noted that his comparative failures are always steps in a new direction, and are almost always followed by some conspicuous victory on the same lines. In any case, they may be counted on the fingers of a single hand. There is certainly no musician, there is probably no artist, whose work as a whole is so varied and yet so masterly.
A complete discussion of musical structure would involve a history of the art from the year 1600. It must therefore suffice for the present purpose to note the main stages of development, and to analyse the chief types, first as they appear in single movements, then as they are combined into the complex organisms of sonata and symphony. Before the Florentine revolution there was virtually no such thing as a system of key-relationship, no recognition of the important effects of contrast which may be produced in a work by the alternation of different tonics. Music during the Ecclesiastical period was entirely homogeneous in structure, bound within the limits of the mode, or, at most, transcending them for a moment of tentative audacity wholly different from the firm definite scheme of modern modulation. When the change came, it was only natural that the first consequence should be a period of chaos. The lay-brothers who had broken loose from the monastery went roaming about the world with no settled plan or direction, turning along any path which promised adventure, and ending their journey wherever they happened to stop at nightfall. The Moresca in Monteverde's Orfeo[11] is a good example of the reaction against uniformity. It can hardly be described without anachronism in our modern terminology, but, if the attempt must be made, we may analyse it as a single melodic phrase, beginning on dominant harmony and ending on tonic, repeated four times in four different keys. In other words, it is as deficient in structural coherence as the preceding method in structural diversity.
But as our scale came into established use, and brought with it an intelligible system of related tonic notes, the value of key distribution began pari passu to be recognised. Men refused any longer to acquiesce in mere indefiniteness or mere monotony, and set themselves to find some means of organising the form of composition by combining different tonal centres into a coherent system. Scientific composers, loyal to the traditions of counterpoint, endeavoured to solve their problem by the elaboration of the fugue in which unity of style is secured by the recurrent subject, and diversity of structure by the free modulation. This form, which may be said to start with the Gabrielis, and to culminate in Sebastian Bach, is of the highest interest to musicians as an attempt to make style and structure play into each other's hands: the former possessing too little diversity, the latter too little coherence to stand as separate organisms. But as it is factitious in its origin, so it is liable to become rigid and mechanical in its results; an exercise of barren ingenuity, not a warm vital expression of true emotion. Bach no doubt could breathe poetry into it, as Corneille could fill with his splendid rhetoric the hard outlines of the classical drama, but both results are great in spite of their form, not in consequence of it. Considered merely as examples of fugue structure, Bach's compositions are not greater than those of a hundred kapellmeisters of his time: they owe their greatness to the purity of their themes, and to the unapproachable perfection of their harmony. But lay aside all questions of melody and harmony, everything, in short, which can be classed under the head of style, and Beethoven's sonatas will still remain supreme in virtue of their structure. Fugue form is an artificial thing which a man can learn: sonata form is a living thing which a man must feel.
Hence it is interesting to notice that all the forms most intimately associated with the sonata may be directly traced to one primitive type of Volkslied.[12] The simplest possible contrast of key which man can adopt without falling into incoherence, is that of a melody in three strains: the first asserting the tonic, the second leading to some related key, the third repeating the tonic in order to complete the outline. Now, if we imagine the first strain given in duplicate, so as to suit the requirements of a four-line stanza of verse, we shall find ourselves with a melodic form of which 'The Bluebells of Scotland' and 'The Vicar of Bray' may be taken as familiar examples. It is probable that the immediate reiteration of the first phrase is a concession to the poet rather than a point of musical structure: in any case, the essential element of the form is to be found in the three clauses, assertion, contrast, and reassertion. 'Of this simple type,' says Dr Parry, 'there are literally thousands of examples.' It is, indeed, the most natural form of melodic sentence which the popular songs of any nation can assume: it is the living germ from which all our most complex musical organisms are developed.
At the outset there are two possible lines of evolution. First, the clause of contrast and the clause of reassertion may be repeated alternately so as to extend the number of strains to five or seven, or whatever is required by the exigencies of the words. Thus we get the primitive type of rondo, which may be illustrated by Burns' 'John Hielandman,' or by the Skye Boat Song, or by our well-known hymn for Palm Sunday. A further stage of development is reached when the number of clauses is fixed at five: and when the fourth, instead of being an exact repetition of the second, affords a change of contrast by presenting a new episode in a new key. This gives us the rondo form as used by Rameau and Purcell, Haydn and Mozart, and occasionally Beethoven himself. We need only compare the exquisite song, 'I attempt from Love's sickness to fly,' with the Adagio of the Sonata Pathétique to see that in point of structure they are identical. No doubt there were some experiments on the way. Haydn tried the form as a vehicle of variations; Mozart opened a new path in his Piano Sonata in A minor: but all these were only variants of the established type which either left its structure unaltered, or remained as exceptions. It was not until the time of Beethoven that the rondo passed into its third stage of development, and even with him the earlier form is of not infrequent occurrence.[13]
Secondly, the number of clauses may be restricted to the original three, and each strain by itself organised into a higher degree of diversity. In its simplest form, which may be exemplified by the minuets of many early sonatas, the first strain ends with a full close in the tonic, and thus, while it fulfils the function of asserting its key, does so at the expense of complete detachment from the second. Hence it is a step towards organisation if the first strain is made to end with a half close, or even to modulate to the key from which the second is going to start. If this is so, the cadence of the third clause will have to be modified—since the tune must end with a full close in the key in which it began—and thus a new element of diversity is introduced into the work as a whole. Of this stage an instance may be found in the Minuet of Haydn's Piano Sonata in D (No. 6), where the first strain is divided into two sub-clauses, one in the tonic, the other in the dominant, and the third strain transposes the latter back and presents both of them in the same key. Here another point offers itself for consideration. If the clause of assertion has been allowed to modulate, and still more, if it has been allowed to dwell upon a key other than the tonic of the piece, it is obvious that the clause of contrast must be allowed still freer modulation—otherwise its purpose will remain unaccomplished. And by this time our clauses have grown in size and extent until it is not appropriate to call them clauses any longer. They have become sentences, or even paragraphs, each with its own subdivisions, its own structural character, and its own function in the general economy of the whole movement. For instance, in the Minuet of Mozart's Piano Sonata in A major, the first part consists of a 10-bar tune in A followed by an 8-bar tune in E: the second begins in B minor, drops to A minor, and then passes through an augmented sixth to the dominant of A, while the third brings the work to a logical conclusion by repeating the two sections of the first in the tonic key.[14]
In its present stage of development the form is admirably suited to the short lyric movements in which it usually appears. Taken by itself it typifies the classical minuet, the air for variations, and the majority of such pianoforte pieces as the Kinderscenen and the Poetische Tonbilder. Extended by the addition of a second example, and completed by a restatement of the first, it gives us the minuet and trio of our sonatas and the common structure of the march and the polonaise. But, as the form grows in bulk and importance, as it discovers new functions and adapts itself to a new environment, so it will naturally submit to certain changes of organism. The two sections of which the first part is composed, appear at present in a direct juxtaposition which will seem crude and disconnected if the movement be increased to a larger size: and it will therefore be advisable to join them by a link of modulation that shall carry the ear gradually over the change of key. Again, the sections of contrast in the second part have hitherto fulfilled their purpose by a complete digression, not only presenting new keys but using them to exhibit new material; and it is obvious that, after the limit of a few bars, such a digression will be fatal to the unity of the work as a whole. Now the variety of key in this part is, as we have already seen, a structural necessity: and thus the readiest means of unification will be attained if we minimise the novelty of material, and use the sections of contrast, either wholly or mainly, to express phrases and themes that have been already stated in the first part of the composition. Lastly, we may notice that the third part ends by repeating in the tonic precisely the same melodic cadence which the first part ended by asserting in the dominant; and it will sometimes happen, that the clause which served admirably as the finish of a paragraph may appear abrupt or inconclusive as the finish of a chapter. In such cases the composer can extend his third part by the addition of an epilogue or coda, completing and rounding off the outline, which would otherwise be left imperfect. It must be remembered that, as a point of structure, the existence of the coda is optional. The composer may wish, for certain reasons of style, to make the first part of his work conclusive, or the last inconclusive: and in either event the need of an epilogue disappears. But, as a general rule, it may be said that the more highly organised the movement the more it will require the employment of this particular device. Continuity is best secured if all the parts of the work be made interdependent, and in that case it is only by a coda that any real climax of phraseology can be attained.
One more detail and the organism is complete. Among the many experiments in structure which mark the course of musical evolution, one of the most important is the so-called French Overture. The main feature of this form, which may be readily illustrated by the Overture to the Messiah, was its habit of prefacing the chief division with an introduction or prologue in slower tempo; and this device has been adopted by the great cyclic composers, and especially by Beethoven, in order to prepare the hearer for movements of unusual importance or solemnity. Like the coda, the introduction is optional in its use: depending not on the structure of the work, but on the manner of its thought and the style of its expression. In Beethoven we find three principal types: the first merely calling attention to the key of the piece, either by directly asserting it, as in the Piano Sonata in F sharp major, or by rousing expectation, as in the third Rasoumoffsky Quartett, the second containing in addition some melodic phrase which is to be employed in the succeeding movement, as in the Sonata Pathétique or the Piano Trio in E flat; and the third, as in the A major Symphony, foreshadowing the key-system, not only of the opening allegro, but of the whole work. It is hardly fantastic to compare the respective prologues of Henry VIII., of Pericles, and of Romeo and Juliet.