harmony
A descending fifths sequence is a common compositional technique used by composers from the eighteenth century to expand a simple melodic or harmonic idea. A typical descending fifths sequence is executed when a short melodic phrase is played over a note (or a collection of notes with emphasis on one in particular) in the bass. The next phrase will virtually be an exact copy of the previous phrase and accompanying bassline, except that it will have been transposed an interval of a diatonic fifth downward or a diatonic fourth upward (either direction will result in the same pitches). In other words, the second phrase will begin at the pitches that would result from moving the first phrase down four notes (or up three notes) within the diatonic scale that the music is in. This process often is repeated multiple times in a single section of the music.
In terms of texture, eighteenth century music often will often incorporate a single melodic line that is accompanied by a more rhythmically simple harmony. This could be described as melody-dominated homophony. With this effect, the listener is drawn solely to the melodic line, with accompaniment only serving to enhance and support the melody. In this example, taken from the beginning of the third movement, “Vivace,” of Johan Helmich Roman’s Symphony No. 3 in B-flat Major, the violin I section carries the active melody, while the rest of the strings and the harpsichord play very simple lines that are often in rhythmic unison with each other and only outline the harmony of the music. This texture helps bring attention to the melody of the violin I section while while emphasizing the harmony of the piece.