A sonata exposition has three jobs: establish the home key, move to and establish a secondary key with a cadence, and lay out the thematic cycle or rotation that will serve as the foundation for the development and recapitulation (Hepokoski & Darcy's "expositional rotation").
In a typical sonata movement, this rotation, and the correlative harmonic scheme, follow a schematic pattern that plays out in the following order:
Such a structure is called a two-part exposition, because the medial caesura divides the exposition into half.
Each of these modules and characteristic cadences are defined in what follows.
Hepokoski and Darcy (whose theory forms the basis of these reference materials) recommend that when analyzing a sonata exposition, "the first task be to locate and identify the treatment of the MC" (p. 24). It is an important event harmonically, in that it marks the point when the secondary key will take over definitively. It is also an important event thematically, because it marks the end of the first part of the exposition and signals the imminent arrival of the secondary theme. It is also an important event rhetorically, because it is typically a high-energy event that has been prepared by significant energy gain in the music that precedes it. Lastly, it is important because the type of cadence used as the MC, and how soon after the opening of the movement the MC occurs, are strong indicators of what kind of music will follow in the rest of the sonata movement.
The most common cadence for an MC is a half cadence, either in the home key (I:HC MC) or the secondary key (V:HC MC or III:HC MC). In the classical era (late eighteenth century), a I:HC MC will usually indicate a shorter, lighter sonata movement. A V:HC MC or III:HC MC will usually indicate a movement of medium length or longer. More formal complexity is likely to come with a V:HC MC or III:HC MC than a I:HC MC.
For a medium–long sonata movement, a V:HC MC or III:HC MC is the first-level default MC type, according to Hepokoski & Darcy. The I:HC MC is a second-level default. For shorter movements, the I:HC MC is the first-level default MC type.
A third-level default would be V:PAC MC or III:PAC MC. A fourth-level default would be a I:PAC MC. These are both considerably rarer than the first and second defaults, and they create a stronger halt in the musical progression.
The musical characteristics that typically surround an MC are: energy gain leading into the cadence (this happens in the TR module, which the MC ends); prominent arrival of a structural dominant; a pause or break in the musical texture (sometimes filled by a single voice or other greatly reduced texture—what H/D call "caesura fill"); and a continuous maintaining of energy between the harmonic cadence and the textural break.
Other common, but by no means required, features are: fa–fi–sol in the bass, leading into the cadence; prolongation or extension of the dominant arrival (what H/D call a "dominant lock"); and/or a thrice-repeated chord of arrival immediately receding the break (what H/D call "hammer blows").
For an MC to be a real MC, it must be followed by a satisfactory S theme (see below). A cadence that otherwise could function as an MC, but is not followed by a satisfactory S theme, is considered a case of "medial caesura declined." Any two-part exposition that declines a medial caesura must contain a "real" MC later. If it does not, it is a continuous, rather than a two-part, exposition (see below).
The EEC is "the first satisfactory PAC within the secondary key that goes on to differening material" (Hepokoski/Darcy, p. 18). It is not optional, and it is always in the secondary key. The Closing module (C) immediately follows the EEC.
It is important to note both that it is the first satisfactory PAC, and that it goes on to differing material. Often the strongest PAC in the dominant is not the EEC. The EEC is a harmonic goal. Once it has been achieved, the process is complete. That harmonic goal may not coincide with the textural climax.
Also, the EEC comes at the end of a theme. Thus, if an S theme reaches a PAC but then repeats itself, the EEC comes at the end of the repeat.
Once the PAC has been achieved, any new material is closing material (C), not new S themes.
A continuous exposition has no MC followed by an S theme. Instead, the TR module gives way to a succession of Fortspinnung modules. Fortspinnung refers to the "spinning out" of a series of related, fragmented melodic units. These are often, but not necessarily, taken from the P theme. Fortspinnung is often associated with TR in general (see below), but in a continuous exposition, the process gets out of control and fails to produce a satisfactory MC. Instead, the motives continue to "spin out" and maintain a high level of energy right up to the EEC, at which point it is too late for an MC or an S theme. Rather than a two-part exposition that follows the model
P TR ' S / C
the continous exposition follows the model
P TR=>FS / C
(The apostrophe stands for the MC; the slash stands for the EEC.)
A continous exposition may present no MC candidates, it may present the possibility of an upcoming MC that is evaded, or it may present an MC that fails to produce a satisfactory S theme (and thus is not really an MC). In each case, an EEC is achieved before any true MC that can produce an S theme.
Another type of continuous exposition occurs when an early PAC in the secondary key occurs with no preceding MC. This PAC is then followed by repeated restatements of the cadential material before a PAC that goes on to new material (the EEC).
In both cases, a clear EEC arrives without any clear MC or S theme. Such situations are continuous expositions.
Sometimes, a composer sets up a two-part exposition, reaches a satisfactory MC, proceeds on to a new theme that sounds like a worthy S module, but that theme degenerates before it can achieve the EEC. In such a case, the degenerated S theme becomes like a new TR and leads into another MC, followed by an S theme that can reach a satisfactory EEC. Hepokoski and Darcy call such a situation a trimodular block (TMB). The three elements of the TMB are the failed S theme (TM1), the dissolution of the failed S (TM2) leading into a new MC, and a new, different S theme that "works" (TM3).
The two MCs tend to adhere to one of the following patterns (the first being by far the most common; H/D, p. 171):
The second MC is called a post-medial caesura (PMC).
The P theme has several functions: establish the home key (with or without a cadence), present the main themeatic material that begins the expositional rotation, and begin the motion toward the MC and the ESC.
A P theme may exhibit any of Caplin's tight-knit forms (sentence, period, hybrid, compound, or small ternary). Sometimes, it can even be a single phrase (antecedent or presentation).
A P theme may be harmonically closed (ending on-tonic) or open (ending off-tonic). A fully closed P theme will end with an authentic cadence, preferably a PAC. However, in the case of P themes that dissolve into TR space, P may simply consist of a presentation phrase or compound basic idea, with no closing cadence. The final cadence of a P module may be elided by the beginning of TR.
The TR module's principal functional roles are to drive toward the MC. This is both a harmonic motion (often involving modulation, if the MC is in the secondary key) and a rhetorical motion, characterized by energy gain. An analysis of a TR module should center around the MC and how the composer approaches the MC.
Following are common techniques associated with TR function.
TR modules often begin with what Hepokoski & Darcy call a "tutti affirmation," particularly in orchestral works. This is a noticeably louder restatement of at least the basic idea of P, before progressing to the MC. They also often exhibit motivic Fortspinnung—a repeated "spinning out" of fragments of a melodic motive, typically taken from the P theme. TR often features melodic or harmonic sequences. Anything else that can be associated with Caplin's continuation function fits transition function, as well—fragmentation, liquidation, acceleration of surface or harmonic rhythm, etc.
We will follow Hepokoski & Darcy's practice of identifying the beginning of TR at the beginning of a phrase. In general, once you hear TR function clearly projected, track back to the beginning of that phrase and label it the beginning of TR.
Hepokoski & Darcy identify several TR types that can be helpful models for identifying TR modules.
An independent TR begins with new thematic material. In other words, it is not P-based. A developmental TR, on the other hand, is P-based. After the end of P (or beginning at the P theme's elided cadence), a developmental TR theme will take ideas from P and work them into a new theme.
Dissolving TR modules all take some part of the P theme and dissolve, degenerate, or liquidate as the module gains energy and moves toward the MC. In the case of a dissolving restatement, P ends and then seems to begin again. This restatement of P dissolves into TR function, and we can subsequently reinterpret the whole theme as a dissolving-restatement type of TR.
In a dissolving consequent, continuation, or hybrid, the P module will consist of the opening phrase of a theme, and the closing phrase of the theme will begin as usual but degenerate into TR rhetoric. The overlap between TR and continuation function make this a particularly smooth transition. A dissolving-reprise TR does the same in the recapitulation (A') module of a small ternary or related form. A dissolving-consequent restatement presents a complete P theme, and then begins a restatement of the consequent or continuation phrase that dissolves into TR rhetoric.
A dissolving P-codetta will introduce post-cadential material to reinforce the cadence at the end of P, and that post-cadential material will dissolve into TR rhetoric.
The chief function of an S module is to bring about a PAC in the secondary key—the essential expositional closure (EEC). Because of its role in relation to this central harmonic event (and its corresponding cadence in the recapitulation, the ESC), the S module is of immense importance and interest in a sonata-form movement. Hepokoski and Darcy go so far as to say that "what happens in S makes a sonata a sonata" (p. 117). How S achieves the EEC, how the recapitulations S module achieves the ESC, and the relationship between the two are among the most defining features of a sonata movement. They are a major focus of a composer's attention, and they should be a major focus of our attention.
The melody of an S module is often straightforward, and typically less memorable than the P theme. This does not take away from its structural importance, however.
The S module in a major-mode sonata movement is typically in the key of the dominant (V). Later works by Beethoven, Schubert, and others play with this exposition, but it is always the first-level default. Early in sonata history it is the only option.
The S module in a minor-mode movement is typically in the mediant (III) or the minor dominant (V, or v if you want to emphasize the minor mode of the secondary key).
Following are several common types of secondary themes:
The definitive characteristics of C are that it follows the EEC, and it is not S. C modules can present wholly new thematic material, or they can borrow from P or TR. They cannot, by definition, be S-based, since that would be a continuation of S. (Keep in mind that the EEC must go on to new material, otherwise the S module continues and the EEC has not been reached yet.)
The C module will always be in the secondary key. It is post-cadential, and the harmonic goal of the exposition has already been reached. If C goes somewhere else, it is not C.
The C module's melodic material can be P-based, TR-based, wholly new, or a string of codettas (short phrase-length units containing flourishes and other stock gestures that each end with a repeat of the PAC in the secondary key).
A retransition is like a turnaround in pop/rock or blues music. It is a dominant chord or arrival in the home key that prepares the return to the home key at the beginning of the repeat of the exposition. The difference between an RT and a turnaround is that an RT follows a modulation. When the RT follows a secondary key of V, it is like a Ponte schema, which turns I/V into V/I by repetition, melodic figuration, or the adding of a chordal seventh.