CHAPTER XVII. THE SONATA-ALLEGRO FORM.
ORIGIN OF THE NAME.—The fully developed Sonata-allegro form is the design in which the classic overture and the first movement of the symphony, sonata and concerto are usually framed. The student must be careful not to confound this musical form with the complete sonata of three or four movements. It is not to be called the "sonata form," but the "sonata-allegro form." It is to one movement only, generally the first one, which is (or was) very commonly an allegro tempo in the sonata and symphony, that the present design refers; and its name, sonata-allegro, is derived from that old historic species of the sonata which consisted originally of but one movement, generally an allegro.
THE SONATA-ALLEGRO FORM.—As distinguished from the sonatine-form, with its two Divisions, this larger species, based upon precisely the same structural idea, has three Divisions,—the Exposition, a middle Division called the Development (growing out of the brief interlude of the sonatine-form), and the Recapitulation. The diagram (the keys of which correspond to the plan of Beethoven, op. 14, No. 2, first movement) is as follows:
| Exposition | Middle Div. | Recapitulation | ||||
| Pr. Th. | Sub. Th. | Codetta | Development, various keys, ending with Retransition | Phr. Th. | Sub. Th. | Codetta and Coda. |
| G maj. | D maj. | D maj. | G maj. | G maj. | G maj. | |
Compare this diagram, also, with that of the Third Rondo-form, and note, accurately, the points of resemblance and contrast.
Compare it, further, with the diagram of the sonatine-form, on page 122. It will be observed that here the Recapitulation does not follow the Exposition at once, as there, but that a complete middle division intervenes, instead of the brief interlude or re-transition; from which the student may conclude that the sonatine-form gradually grows into the sonata-allegro form, as this interlude becomes longer, more elaborate, and more like an independent division of the design. Or inversely, and perhaps more correctly, the sonata-allegro becomes a sonatine-design by the omission (or contraction) of the middle Division.
THE EXPOSITION.—The presentation of the thematic factors, the statement or Exposition of the two themes and codetta, is made exactly as in the sonatine-form, though probably upon a broader scale. The Principal theme is usually a Two-Part Song-form, at least; often Three-Part. In broader designs, a separate transitional passage appears; in more concise designs, the transition is developed out of the last Part of the Principal theme by the process of dissolution—as will be seen. The object of the transition is, as usual, to lead into the new key (of the Subordinate theme). It is sometimes, though very rarely, omitted.
The Subordinate theme contrasts notably with its fellow, but asserts equal importance, as a rule, and may be of equal, or nearly equal, length. The addition of a codetta is almost indispensable, and frequently two or more appear, growing successively shorter, and generally repeated. In the sonata-allegro the Exposition closes, as a rule, with a very decisive perfect cadence, followed by a double-bar, and—especially in older sonatas—repetition-marks; the repetition of the Exposition being justly considered important, as a means of emphasizing the "statement," and enforcing the hearer's attention to the thematic contents before preceding to their development in the second division of the form. In the sonatine-form, on the contrary, this positive termination of the Exposition (and consequently the double-bar and repetition) will very rarely be found.
THE DEVELOPMENT, OR MIDDLE DIVISION. The second division of the sonata-allegro form is devoted to a more or less extensive and elaborate manipulation and combination of such figures, motives, phrases or Parts of the Exposition as prove inviting and convenient for the purpose, or challenge the imaginative faculty of the composer. In this division, opportunity is provided for the exhibition of technical skill, imagination and emotional passion; for the creation of ingenious contrasts and climaxes, and, in a word, for the development of unexpected resources not strikingly manifest in the more sober presentation of the thematic factors during the Exposition. The intermingling of new material is naturally also involved in the process of development; sometimes to such an extent that the new predominates over the old,—in which case the middle Division is more properly called an EPISODE.
This second Division of the sonata-allegro form (the Development or Episode) corresponds precisely, as will be recognized, to the second Part of the Three-Part Song-form; consequently, it represents the "departure" (see page 90), and entails, in rational form, the significant "return" to the beginning. Further, it matches to some degree the "digression" in the rondo-forms. At all events, its important structural function is to establish contrast; and the necessity for corroboration of the leading thematic ideas—in consequence of this contrast—is satisfied in the Division which succeeds.
It is sometimes possible to mark the exact point where the Development ends and the process of re-transition commences; but usually the return to the beginning is accomplished so gradually that no sensible interruption occurs.
THE RECAPITULATION.—This, the third Division, is, as usual, a review of the original presentation of the thematic material,—the recurrence of the Exposition. It is sometimes a nearly exact reproduction, excepting the necessary change of key in the Subordinate theme and codetta, and such modification of the transitional section as may be thereby involved. Sometimes, however, considerable alteration is made, at times so elaborate (especially in broader examples) that, though preserving easy recognizability, the Recapitulation assumes the appearance of a new version of the Exposition, and becomes a more independent part of the design.
A coda is almost always added; sometimes brief, but occasionally so elaborate and extensive as to merit the appellation "second Development."
DISSOLUTION.—When any section of a higher form starts out with a perfectly definite structural intention, pursues this intention for a time (sufficient to establish it), but then insensibly diverges and gradually adopts a new modulatory direction,—as transition into the following section,—the form is said to be dissolved. Such dissolution takes place, naturally, within the later section of the theme, or Part, or whatever it may be, whose actual, definite ending in the expected key is thus frustrated. For instance, the second (or third) Part of a theme may be dissolved; or the last phrase of a period or double-period; or the repetition of a phrase. And the dissolution is invariably applied before a transition or re-transition, as a means of interlocking the factors of the form more closely and coherently. Therefore it is a process peculiarly adapted to the higher designs of composition, and is seldom omitted in the sonata-allegro form. For an illustration, see Beethoven's sonata, op. 14, No. 2, first movement: The Principal theme is a Two-Part Song-form; Part I, a period, from measures 1 to 8; Part II begins in measure 9, and has every appearance of becoming also a period; its Antecedent phrase closes in measure 12, its Consequent begins in measure 13—but its end, as Second Part, in the usual definite manner, cannot be indicated; the key is quietly changed from G to D, and then to A, in obedience to the call of the Subordinate theme (beginning in measure 26), into which these last 10 or 12 measures have evidently been a Transition. The Second Part of the Principal theme therefore includes the transition; but where the Second Part (as such) ends, and the transition (as such) begins, it is impossible to point out accurately. The definition of this Principal theme is, "Two-Part form with dissolved Second Part," or, still better, "with transitional Second Part."
In our illustration of the sonata-allegro form it is necessary, on account of limited space, to select a very concise example, of unusual brevity,—Beethoven, sonata, op. 49, No. 1, first movement; the original may be referred to, for the omitted details:—
