First theme group
The first theme of sonata form.
What it means
The first theme group (German Hauptsatz) is in the study of the form of the sonata movement the first thematic section of the exposition. It stands in the home key and presents the material that shapes the character of the movement. Its counterpart is the second theme group (Seitensatz), which stands in another key and often forms a contrast. The term “Hauptthema” (main theme) designates largely the same; “Hauptsatz” rather stresses the whole section, “Hauptthema” rather the thematic idea itself.
Musical use
The first theme group has the task of consolidating the home key and setting up a pregnant idea that remains recognizable in the course. It is often built as a period or as a Satz (sentence): in the first case antecedent and consequent stand opposite one another like question and answer, in the second a short basic idea is repeated and then spun on. Both models allow numerous variations.
The first theme group is followed by a transition that modulates to the key of the second theme group. The boundary between the two is not always sharp; at times the transition begins with material of the first theme group, which is then led in the new direction.
In the development, motifs of the first theme group are often broken up and worked out, and in the recapitulation it returns in the home key. Its return is one of the clearest points of articulation of the form.
Note that “Satz” has several meanings in German music terminology — as a part of a multi-movement work, as a setting in the sense of a composition (Tonsatz), and as a formal model. The Hauptsatz here means the thematic section within a movement.
In the Classical period the first theme group is usually built as a period or sentence and ends in the home key, often with a half cadence. A transition then leads to the second theme group. The first theme group supplies the material from which the development mainly draws.
Performance practice
Shape the first theme group with a clear profile, for everything else refers to it. Impress its motifs on yourself so that you recognize them in the development. And shape its return in the recapitulation as an arrival, not as a mere repetition.