The double neighbor

Both neighbors taken at once: the line steps off a held tone to one neighbor, leaps a third across to the opposite neighbor, and returns to the tone it decorated. Two dissonances stand in a row — licensed because the frame is static: the main tone before and after is the same consonance, so the ear hears an orbit around a fixed point rather than motion that fails to arrive. The figure belongs to the quicker species, on weak quarters, with the return mandatory.

The tightest way to sustain interest on a stationary tone: where a single neighbor is a nod, the double neighbor is a full turn, and it became the seed of the written-out turn ornament. It suits quick species and florid lines wherever the harmony parks on one chord for a bar and the melody must keep moving without going anywhere.

• Failing to return to the decorated tone, which turns an orbit into two stranded dissonances.
• Placing the figure across a change of harmony, where the frame tone is no longer the same consonance on both sides.
• Beginning the figure so a dissonance takes the strong beat, an accent the ornament has not earned.
• Widening the middle leap past a third, which breaks the figure into an unrelated neighbor and leap.

• Johann Georg Albrechtsberger, Gründliche Anweisung zur Composition (1790), The counterpoint chapters, third species (changing notes) — The Classical-era account of the paired-neighbor figure inside the quarter-note species.
• Ebenezer Prout, Harmony: Its Theory and Practice (1889), The chapter on auxiliary notes and anticipations — The double auxiliary codified for the harmony classroom, return required.