If you’re like me and you actually read program notes and CD inserts for fun, you’ve probably run across the phrase “sonata form” (or “sonata-allegro form”) to describe many movements of the works being written about. If you’ve never taken a formal class in music theory (or, more specifically, music theory as relates to high-prestige music being written in Europe from 1750 or so to around the outbreak of World War One), this probably hasn’t been a terribly useful descriptor. Like so many pieces of jargon, “sonata form” is a clean, concise way of describing a rather complicated thing that provides all the information necessary for those in the know and almost no information at all for those who aren’t. Today I’m going to do my best to explain what sonata form is in a way that’s accessible to people with a minimum of broader music theory background.

Sonata form, fundamentally, is a way of structuring a (relatively) large-scale piece of instrumental music. It dictates, with varying degrees of strictness, how many themes you’re likely to get, when those themes are likely to appear, and other things of that nature. It emerged very gradually around the middle of the 18th Century, and if its exact origins are somewhat murky, it was well enough established by the later parts of the 1700s that Mozart, Haydn, and Beethoven all used it in their symphonies, sonatas, and string quartets. These three composers being three of the most venerated and studied composers in the European repertory, by the 1820s or so, music theorists were already picking apart their works and coming up with theories to explain what was going on.

This is where the trouble starts. Because, while those theorists were often correct in the broad-strokes picture of late-1700s musical practice, their assessments of the finer details aren’t always that well supported by the actual music of that time. But then, naturally enough, composers of the mid 1800s turned to those theoreticians to help make sense of the works of their compositional predecessors, and started writing works with those historically uneven 1820s descriptions of sonata form as guides, meaning that those descriptions are sometimes a better fit for music written after they were developed than they are for the music they were developed to describe. Rinse, wash, and repeat for several generations, and the people still writing in sonata form in the 1910s are doing so in ways that are, at times, radically different than those who originated the form in the 1750s.

Coming up with a theory that can adequately deal with this diversity of practice is obviously a tall order. On the one hand, there clearly is substantial similarity among all these movements, and likewise there's a clear line of conscious continuity of compositional practice, but there are enough differences that simple theories are woefully inadequate to explain the bewildering diversity at hand.

Unsurprisingly, this has led to several camps of theorists who take rather different approaches to explaining what’s going on. Many encyclopedia articles on sonata form try to give equal time to a number of these camps, which is entirely appropriate for the core encyclopedic endeavor of cataloguing knowledge. But given the arcane and jargonistic nature of the disputes between these theoretical camps, doing justice to each of them in an article makes that article nigh incomprehensible for a neophyte, and the result is that most encyclopedia articles are actually not a great place to start if you’re just trying to come to terms with the basics of the form.

As such, I want to be very transparent about my bias: I’m writing this post using the framework developed by James Hepokoski and William Darcy in their Elements of Sonata Theory. This is what I was taught in the music theory courses I took in college, and it’s what I was exposed to in the history sequence as well, which is maximally unsurprising because the pertinent courses in that sequence are taught by James Hepokoski himself. I’ve found it tremendously useful when listening to works written in sonata form, and I think it’s flexible enough to cover the diversity of sonata-form practice without falling to pieces. There are professional theoreticians out there who would disagree with some of the details of what I’m about to say, but if they attack you for following two of the most eminent scholars in the field, they’re honestly just being dicks and you should ignore them.

There are two key things that are central to understanding sonata form. The first is that sonata form is a goal-directed form. Sonata-form movements are trying to accomplish a specific musical task: Confirming the key of the movement with a specific cadence. What does this mean?

In music of the sort that uses sonata form, there's one pitch that serves as a home base; it’s the central reference point, and all the other pitches have roles that are defined in terms of how they relate to it. This pitch is called the tonic, and it’s synonymous with the key of the piece. (So a piece that is “in G” will use the pitch “G” as the tonic.) You can get a sense of this yourself with something as simple as “Row, Row, Row Your Boat”: If you try to stop singing on “stream”, something feels unfinished, incomplete. It’s only when you get all the way to “dream” that the piece feels satisfyingly complete. “Dream” is sung on the tonic for that piece, and that’s what gives it that sense of finality. That’s a very simple example, but the same principle holds in much more complicated music.

One of the things that makes complicated music complicated is that the tonic can shift. We might start out feeling like G is our home base, but a certain sequence of notes can make us feel like D is our home base. Some of these shifts are very fleeting, but some of them are considerably longer; the easiest way to mark one of these shifts as more than a temporary, fleeting feint in the direction of that new key is to confirm the shift (or modulation) with a cadence. A cadence is a short sequence of chords that comes at the end of a musical phrase and provides a sense of closure. If a piece of music cadences in a key, then it is confirmed as being in that key, at least temporarily. The goal of a sonata-form movement is to secure a specific cadence in the home key of the movement in such a way that that key is confirmed with a great deal of finality and certainty indeed. (There will be more on this specific aspect of sonata form below, once we get to the walk-thru. For now, the big takeaway is that a sonata-form movement is out to achieve a strong and final sense of harmonic closure and completeness in the key that it started in.)

The second key to understanding sonata theory is that sonata form is less a strict outline for how to organize a movement and more a set of defaults or expectations where any given movement will adhere to some of them and not to others. Think of it like describing the plot of a “typical” X-Files episode. Most of them start in medias res with someone we’ve never seen before in a scene of relative isolation, they then get attacked by the monster of the week, then the title sequence plays. Mulder tells Scully about the case, and they head out to the scene to investigate. Scully is resistant to Mulder’s theory, but in doing an autopsy on the victim’s body, she finds evidence that is strongly at odds with the mundane theory of how the victim died, evidence that seems to be compatible with Mulder’s theory instead. And so on, and so on, up to the final shot that implies the defeated monster of the week might not be so permanently defeated after all.

Now, no single episode is going to hit all of these plot points exactly in sequence — that would be hella boring! Individual episodes might hit some of these, bypass others, and, as a delicious surprise, deliberately subvert others still (the seeming victim before the credit drop is actually the monster!). But those subversions and aversions only have the impact that they do because we have a pretty robust sense of what usually happens at any given point in an X-Files episode.

Sonata form works in much the same way. Once you’re familiar with how it works, you expect certain things to happen at certain points in a sonata-form movement. In any given sonata-form movement, some of those expectations are going to be fulfilled without trouble, but some of them are going to be toyed with or even thwarted outright, with results that can range from witty and humorous to uncomfortable or even tragic. Much of the power of these movements comes from the way they fulfill or subvert expectations, and being alive to the expectations of the form will only enhance your appreciation for this music.

(A necessary aside: Sometimes, instead of starting with the untimely demise of the monster of the week’s latest victim, an X-File episode will start with surreal imagery and a trippy New-Agey voiceover. This marks the episode as belonging to one of the various mythology arcs, and sets up a substantially different set of expectations about what’s likely to happen in the plot. Likewise, there are second-level (and third-level, and . . . ) sets of expectations about what can happen in a sonata-form movement if the most common thing doesn’t happen. There simply isn’t room to get into all of those alternatives in this post — Hepokoski and Darcy spend 621 dense pages delving into these alternatives, and even their work is not exhaustive. I’m only going to be covering the most common, first-level, default expectations in this post, but understand that there are many common alternative possibilities that I’m going to be passing over without mentioning. This is an introduction to Sonata Theory, not an exhaustive treatise on it.)

So with all that throat-clearing out of the way, let’s look at a sonata-form movement and see how it ticks! I’m going to be describing the form using time stamps in reference to this recording of the first movement of Mozart’s 40th symphony. As implied by the above, there are ways that this movement deviates from the default expectations, but that’s true of basically every sonata-form movement ever, so it’ll still work well as an example.

Some sonata-form movements, especially first movements, begin with an introduction that’s not part of the sonata-form proper. Usually these introductions are slower than the body of the movement, but beyond that there’s a lot of variation; there aren’t strong expectations for what an introduction looks like, so generalizing about them is difficult. They can still be Analytically Significant, but usually you have to deal with them on a case-by-case basis. The movement we’re looking at today doesn’t have one, but instead plunges at 0'00'' into the exposition.

The exposition is the first of three large sections in a sonata-form movement, and its main job is to present the musical materials that will be used to build the rest of the movement. The first thing that happens in the exposition is the primary thematic material. This name can be a little misleading: It’s not called primary because it’s necessarily the most important material in the movement, it’s just called that because it comes first. In the Mozart example, this is the theme that starts in the violins (“It’s a bird, it’s a plane, no it’s Mozart!”), and continues thru the woodwind interjection at 0'13''. At the 0'21'' mark, the violins re-start this theme, but something is different now: We’ve started getting those modulatory shifts I talked about above — we’re being slowly pushed away from G Minor.

That’s because we’ve moved into the next zone of the exposition, the transition. The transition (TR if you’re fancy) is a section that gains in energy and is, in some sense, an affirmation of the music laid out in the primary thematic material zone (P-space if you’re fancy). If that first zone says “Hey, I thought we could maybe do a sonata-form movement?”, the transition says “Yes! That is an excellent idea! Let’s do it!”. The transition also usually modulates to a new key area, giving us a new pitch to use, temporarily, for our home base. As with the Mozart, transitions often use the primary thematic material, but it’s not uncommon for them to introduce new themes as well, and indeed at 0'29'' a brassy new theme comes bursting forth to drive the movement forward.

At 0'44'', the music comes to a dead halt. This is the medial caesura, and it’s an important structural moment. It separates the first half of the exposition from the second half, and clears the plate for what’s about to happen. They aren’t always dead silences — sometimes there’s generic filler fluff — but they’re always occasions to pause for breath before plunging on with the exposition.

But plunge ahead we do, into the secondary thematic material (S-space), which begins at 0'46''. You’ll notice that we’ve shifted from a dreary minor to a sunnier major; that is a very strong expectation for movements of this era that start in the minor mode. Just like we want books and movies to have happy endings, composers in the Classical era (and beyond) usually wanted their works to move from sadness into joy. (In a major-mode work, we would still expect this secondary theme to be in the major; moving from major to minor would be highly surprising, tho of course there are examples where it happens.) Either way, we expect the secondary theme to be in a new key, and getting this theme from the new key back to the key of the primary theme is the core task of a sonata-form movement.

Remember above how I mentioned that “primary” in this context means “first” and not “most important”? That’s true with a vengeance for “secondary”. The secondary thematic zone is the one that has to carry out the key task of the movement: Securing a cadence to confirm the key. As we get further into the 19th Century, theoreticians and composers will start to conceptualize the primary theme as rhythmically active or “masculine” and the secondary theme as lyrical or “feminine”, with all of the loaded sexist baggage that those dichotomies imply. That conceptualization may be appropriate for the works of people like Wagner, but it simply does not hold for earlier composers in any meaningful way. Even in those later works, however, it’s still the secondary theme that’s tasked with securing the mission-critical cadence.

In the Mozart, that cadence happens at the 1'11'' mark. There are a number of nitty-gritty technical concerns that can need to be fulfilled to make a cadence the real one (the essential expositional closure or EEC), but a good rule of thumb is that the essential expositional closure is the first cadence that isn’t followed by a repeat of the secondary theme. So, while we do get a cadence at 0'54'', that cadence is followed by a repeat of the secondary theme, implying that it didn’t quite work to seal the deal. The cadence at 1'11'', however, is followed by a new theme (a bold rising figure in the lower strings), so we know that the secondary theme has succeeded in doing its job.

This new theme marks the beginning of the closing section or C-space (sometimes also known as the “codetta” and described as a “landing strip”). C-space is usually kind of light and fluffy, a celebration of having attained the EEC, and it very frequently brings back snippets of the primary theme. Mozart does the primary theme thing (you can here the first echoes of it at 1'19''), but this closing section is unusually long — it runs until 1'48'', which is far more than one would normally expect from the brevity of the primary, transition, and secondary zones. If we were doing a full analysis of this movement, that disparity would be something worth noting and looking for explanations for, but since that’s not what we’re out to do today, we’ll merely mention it and move along.

The entire exposition — primary theme, transition, medial caesura, secondary theme, EEC, closing space — then repeats verbatim. Composers in later eras will do away with this repeat, and following that trend, some contemporary performers will retroactively ignore it in works from the 18th Century, but the Classical style is all about form and structure, and the repeat serves an important function in demarcating the exposition as a self-contained referential unit, so skipping it is honestly a pretty questionable interpretive choice.

After the exposition comes the next big formal section, the development. The development takes the materials from the exposition and develops them, breaking them apart, rearranging them, and otherwise teasing out their musical possibilities. This is a pretty free-form process and individual development sections vary much more wildly than individual expositions, so the formal expectations for this section are considerably weaker.

There are, however, a few things we can say. It is very common for development sections to start with material from the primary thematic zone, and it is likewise common for developments to move thru the zones of the exposition in order. The development may spend a long time making contortions out of the primary theme, but once it’s started playing around with material from the transition, it’s uncommon for it to move backwards and return to messing about with the primary theme again. In addition, it’s not uncommon for developments to not make it all the way thru all of the themes from the exposition — many developments only develop the primary and transitional themes, omitting the secondary and closing materials entirely. This isn’t all that surprising considering the role of the secondary theme: It’s the theme that ultimately has to confirm the key of the piece, so bringing it in in the middle of the development (which we expect to wander into numerous fleeting other keys) risks doing that too early and lending undue weight to an incidental excursion.

Mozart’s development section begins at 3'39'', and it’s entirely occupied with the primary theme. Since, again, I’m only using this as an example to illustrate the form and not doing a full analysis of the piece itself, I’m not going to spend a lot of time here, but it’s worth listening to just to get a sense of the storminess and abrupt changes that are typical of developmental sections.

At the very end of the development, we return to the land where expectations exist. Specifically, we expect the bass to get stuck on one note and hold it out, either as a continuous long tone or with an obsessively repeated rhythmic figure. This is called a dominant lock, and it can sometimes be hard to hear if you don’t have a lot of experience listening for such things, but if you can pick it out, it’s a giant signal that we’re coming up to the end of the development and preparing the way for the recapitulation that follows. In the Mozart example, it starts to emerge from the prevailing texture at around 4'32'' and really gets going at 4'44''. The upper voices may still be doing quite elaborate figuration, but once the bass runs aground on that fixed point, the next steps are pretty inevitable.

The task of the recapitulation is to cycle thru the same materials as the exposition, but this time getting the secondary theme to happen in the same key as the primary theme. So we begin, at 4'51'', with a repeat of the primary theme from the exposition, now back in our home key of G minor. The transition at 5'11'' starts exactly as it did in the exposition, but it soon deviates from a perfect repetition. This is as expected. After all, in the exposition, the transition served to push us away from G, and now we want it to keep us there. Often this results in a shorter transition, but Mozart instead opts to expand it considerably.

Around 5'46'', however, the music should start sounding familiar again. Having worked out an alternate transition that keeps us in the home key, the tail end of the transition in the recapitulation almost always snaps back at a certain point (the crux) to being an exact repetition of the version in the exposition. In some sonata-form movements, the rest of the recapitulation follows suit, with the secondary and closing materials being an exact transposition from their first appearances, but in others Shenanigans Ensue, shenanigans that often serve to mark passages for theoretical scrutiny.

The Mozart falls into this latter group. We get our medial caesura just as expected at 5'54'', but then something goes wrong. Instead of the secondary theme unfolding in the expected G major, it happens in G minor instead. This is a subversion of our expectations, and is definitely something that any analysis of this piece would have to dig into. Just as in the exposition, we get a second statement of the secondary theme at 6'06'', but it can’t shake the minor mode, and the critical cadence, here the essential structural closure that is the ultimate goal of the entire movement, occurs in G minor at 6'27''. (If you’re paying close attention, you’ll notice that there’s an additional interjection here that wasn’t there in the exposition. A standard interpretation of this would be as some kind of last-ditch attempt to force the piece into the major.) The closing section then returns, now expanded to even larger proportions than it occupied in the exposition. Despite having an identical substructure to the exposition, the recapitulation is not repeated, tho some early sonata-form movements do call for a repeat of the entire development+recapitulation sequence.

Just as there is sometimes an introduction before the sonata-form proper, there is sometimes a coda after it. As with introductions, it’s hard to make many generalizations about codas, beyond saying that they’re usually in the main tempo of the movement. This movement has neither.

And that, in a (rather large) nutshell, is sonata form! A repeated exposition consisting of a primary theme, a transition, a medial caesura, a secondary theme, an essential expositional closure, and a closing theme; a free-form development that ends with a dominant lock in the bass; and a recapitulation that works its way thru the same materials in the same sequence as the exposition, but alters them to bring the secondary theme into the same key as the primary theme and convert the EEC into the essential structural closure that confirms that key as firmly in place. There are countless variations on this basic structure, but this is a framework that should stand you in good stead the next time you encounter a work that’s in this form.