At this point, however, a confusion is likely to arise from the fact that the term "sonata" is used in two senses. It means sometimes a complete piece of music in three or more distinct movements; at other times it means a scheme or plan of musical structure exemplified in one or more of these movements, usually the first. When used in this sense it is generally coupled with the word "form": this is the way in which we shall use it here, letting "sonata-form" mean this peculiar type of musical structure, to be described in detail presently, while using "sonata" alone to name a complete composition of which one or more movements are in "sonata-form."
The sonata, as written by Philip Emanuel Bach, Haydn, Mozart, Beethoven, and modern composers, usually contains some movements in forms more primitive than "sonata-form," and already familiar to us. Thus the minuet, which often appears as the second or third movement of a sonata, has changed little since Mozart's day; the rondo, frequently used in the finale of a sonata, remains in all essentials as it is presented in the last diagram of Chapter VI; and the theme and variations, so far as its formal plan is concerned, has remained very much as Haydn left it, although, in common with the rondo, it has been vastly enriched in content and diversified in style by the genius of Beethoven.
II. ESSENTIALS OF SONATA-FORM.
The element of true novelty in sonatas is to be found, not in these primitive movements, but rather in those movements which are in "sonata-form," and which show a breadth of conception and an elaboration in development never found in simple lyric forms like the minuet. This breadth and elaboration is always the result of a germination of musical thought, such as we have already often mentioned, and by virtue of which alone a composition can take on real grandeur of proportions. The essentials of sonata-form are (1) the presentation of two or more themes or subjects in that section known as the Exposition, and symbolized in our diagrams by the letter A; (2) the evolution of these themes, by means of melodic germination, in that section known as the Development, and symbolized by B; and (3) the restatement of the original themes, rounding out the movement symmetrically, in the section known as the Recapitulation, and symbolized again by A on account of its practical identity with the Exposition. It matters not which movement of a sonata takes this characteristic form, whether, as in the majority of cases, it is the first (whence the term "first-movement form," often used as a synonym for "sonata-form") or the slow movement, as often happens, or the finale. Wherever sonata-form exists we find this three-part sectional structure, resulting from the natural germination in the middle section of the musical ideas stated in the first, followed by their restatement in the third section.
The reader may ask at this point, in what respect such a form differs from the simple ternary form illustrated in a minuet, for example, wherein the second section usually contains some development of the theme, and the third some recapitulation. The answer is that in the sonata-form the enlargement of the proportions throughout results, first, in the substitution of complete and more or less contrasting themes, for the rather slight musical subject of a minuet, and second, in the substitution of a long and elaborate development of these themes for the rather casual and superficial modification of the subject which forms the second section of a minuet. Moreover, in the sonata-form a novel feature is the contrast introduced by making the first section embody duality of key (first theme in tonic, second in related key) while the third section, by presenting both themes in the tonic, embodies unity of key. Nevertheless it remains true that sonata-form is, both logically and historically, a development of such simple forms as we have in the minuet, as is indicated by the name of "developed ternary form" often given to it.[22]
Sonata-form is thus but an extreme application of certain essential principles of structure exemplified in simple ways in other more primitive musical forms, and for that matter in many other departments of life. It is perhaps not over-fanciful to discover the same principles in the construction of a novel, in which we often find: first, the presentation of certain characters, more or less in antagonism; second, the development of the plot and of the characters themselves; and third, the reconciliation of the characters in the denouement. Similarly, a sermon consists of (1) the assertion of a text or subject of discourse, (2) the illustration of its truth by examples and other elucidations of what is implied in it, and (3) a final restatement of it with the greater force made possible by its discussion. Or again, we may see striking analogies to the artistic form we are considering in such processes of nature as the budding, flowering, and death of a plant, or in human life with its youth, its period of activity, and its time of retrospect.
III. A SONATA BY PHILIP EMANUEL BACH.
Sonata-form, historically speaking, first takes definite shape in the work of Philip Emanuel Bach (1714-1788), the most distinguished of the sons of the great Sebastian Bach. Though not a man of the highest creative genius, C. P. E. Bach possessed an ingenuity and a pioneering spirit which led him to make innovations so important that Haydn and Mozart freely acknowledged their debt to him. Feeling that music in the polyphonic style had reached its full development, he was original and adventurous enough to seek new means of expression and a novel combination of features of style already familiar.
In order to understand the situation that confronted him we must put aside temporarily the impressions we have received from the Andante of Haydn and the Rondo of Mozart, since both these compositions were produced at a time when his influence had already made itself felt. He had to face the problem of writing instrumental music that should be free from the constraining influence of the dance, of polyphonic style, and of the elaborately ornamented style of operatic music. He had also to find out how to unify a long piece of instrumental music by co-ordinating all its parts. The only solution of these problems lay in inventing what might be called pure instrumental melody: i. e., melody that was essentially expressive in the particular medium employed—the piano, the violin, the orchestra—and that was unhampered either by strict poetic or dance forms, or by the peculiar phraseology of polyphony. He did not, to be sure, entirely achieve this; we find evidences of both the older styles in his music. But an examination of any instrumental masterpiece of Beethoven will reveal how much he owed to the pioneer labors of C. P. E. Bach.