Sonata-allegro form is one of the most significant forms of the Classical era. Because of its importance we’ll have multiple reading items on the topic. This first link will take you to a very brief definition of the form. There are melodic and harmonic elements to sonata-allegro form, but the most important thing for us to understand for the purposes of this class is its structure.
Let’s flesh out the definition you’ve just read. There are common melodic and harmonic practices within this form, the explanation of which requires a deeper understanding of music theory than is required for this class. This brief introduction will suffice for our purposes.
Sonata form (also sonata-allegro form or first movement form) is a large-scale musical structure used widely since the middle of the 18th century (the early Classical period).
While it is typically used in the first movement of multi-movement pieces, it is sometimes used in subsequent movements as well—particularly the final movement. The teaching of sonata form in music theory rests on a standard definition and a series of hypotheses about the underlying reasons for the durability and variety of the form—a definition that arose in the second quarter of the 19th century. There is little disagreement that on the largest level, the form consists of three main sections: an exposition, a development, and a recapitulation; however, beneath this, sonata form is difficult to pin down in a single model.
The standard definition focuses on the thematic and harmonic organization of tonal materials that are presented in an exposition, elaborated and contrasted in a development and then resolved harmonically and thematically in are capitulation. In addition, the standard definition recognizes that an introduction and a coda may be present. Each of the sections is often further divided or characterized by the particular means by which it accomplishes its function in the form.
Since its establishment, the sonata form became the most common form in the first movement of works entitled “sonata,” as well as other long works of classical music, including the symphony, concerto, string quartet, and so on. Accordingly, there is a large body of theory on what unifies and distinguishes practice in the sonata form, both within eras and between eras. Even works that do not adhere to the standard description of a sonata form often present analogous structures or can be analyzed as elaborations or expansions of the standard description of sonata form.
Here’s one more look at sonata form: a video lecture by Dr. Craig Wright at Yale University. In his presentation, he relates sonata form to some of the musical structures you may have come across in popular music. He also begins to explain some of the most common melodic and harmonic practices associated with sonata form. This lecture is also available directly through YouTube, but the Yale page we’ve linked to makes it provides a transcript of the lecture and the ability to download the entire presentation if you’d like.