Origins of Sonata Form

Defining Sonata-allegro form is easy, save for all the exceptions. One must regard an effort to arrive at a description of where this form came from with an ear to what might have been the expectations that were set up in the history of its use, and then just as quickly discuss all the ways these expectations are played with, and that leads to discovery of the vitality of the form. Like another great form and procedure of music, fugue, the life in it lay in its flexibility not in how strictly it is defined. Since its use if most often tied to harmony see my article on harmony for a discussion of chord names and scale degrees if this terminology is not familiar to you.

Sonata-Allegro form has its roots in Baroque forms such as the Aria de Capo, that is, the aria as written by Bach and Handel with a repeat of the introduction and beginning of the vocal part, and a related form such as one finds in pieces like Bach's Keyboard music, such as the first movement of the B-Flat Partita.

These works have a harmonic plan that eventually leads to Sonata-Allegro form. They begin, establishing a key, a tonic key (I), in the Bach Partita, B-Flat, and modulate to the key of the dominant (V), in this case F-Major. In this keyboard work there is a repeat of the first section, or reprise. What follows is a modulation to some relatively distant key, sometimes just the relative-minor (iv) or even more far afield. This is called the "Point Furthest Removed" or "X section", it is followed by a modulation back to the material and key of the beginning (I). It is often followed by a wrenching of the modulation that originally went to V to end on the tonic (I). The second section is often also repeated in the keyboard work. The Aria has the repeat be the part played "from the top', 'de capo' be the completion of the form with the first modulation away from the tonic resolved. It is important to point out that these Baroque forms did not have much melodic or textural contrast between the "key Areas" of the form.

Development of Sonata-Allegro from from Baroque forms

Sonata-Allegro form develops from the harmonic plan of older Baroque forms by putting in a whole set of conventional contrasts that signal modulation and arrival.