Imperfection (mensural notation)
In mensural notation, the twofold (instead of threefold) value of an otherwise perfect note.
What it means
Imperfection denotes, in the mensural notation of the Middle Ages and the Renaissance, the twofold value of a note that otherwise counts as perfect, that is, threefold. A note that normally divides into three smaller values is shortened by imperfection to two smaller values.
Musical use
In mensural notation the threefold, “perfect” division of a note value was the default case, unless contrary signs or contexts indicated otherwise. Certain rules and signs, such as the proximity of smaller notes or special dots, could, however, “imperfect” a note, that is, reduce it to twofold value. This system of perfection and imperfection was complex and differed across various periods and regions of mensural notation.
Imperfection should be distinguished from perfection, the regular threefold value, and from the later customary dotting, which in modern notation deliberately lengthens a note by half instead of shortening it. The concept concerns exclusively the older mensural notation, not today's staff notation.
Performance practice
When reading or transcribing mensural notation, first clarify whether the piece is based on a fundamentally twofold or threefold mensuration, and then check individual cases of imperfection against the contemporary rules. For practical performance, a modern transcription that has already resolved these subtleties is usually worthwhile.