As used in the 17th century, the term "well tempered" meant that the twelve notes per
octave of the standard keyboard were tuned in such a way that it was possible to play music in all
major or
minor keys that were commonly in use, without sounding perceptibly out of tune. One of the first attestations of the concept of "well tempered" is found in a treatise in German by the music theorist
Andreas Werckmeister. In the subtitle of his
Orgelprobe, from 1681, he writes: The words and were subsequently combined into . A modern definition of "well temperament", from
Herbert Kelletat, is given below: : In most tuning systems used before 1700, one or more intervals on the twelve-note keyboard were so far from any
pure interval that they were unusable in
harmony and were called a "
wolf interval". Until about 1650 the most common keyboard temperament was
quarter-comma meantone, in which the
fifths were narrowed so as to maximize the number of pure
major thirds.
Syntonic commas were distributed across most sequences of four narrowed fifths, with one remaining correction accommodated usually in the diminished sixth
G to
E, which expands to almost a justly tuned
minor sixth. It is this interval that is usually called the "
wolf", because it is so far from
consonance. The wolf was not a problem if music was played in a small number of keys (or to be more precise, transposed
modes) with few
accidentals, but it prevented players from
transposing and
modulating freely. Some instrument-makers sought to remedy the problem by introducing more than twelve notes per octave, producing
enharmonic keyboards which could provide, for example, a D and an E with different pitches so that the thirds B–D and E–G could both be euphonious. These solutions could include
split keys and multiple
manuals; one such solution, the
archicembalo, was mentioned by
Nicola Vicentino in 1555. However, Werckmeister realised that split keys, or "subsemitonia" as he called them, were unnecessary, and even counterproductive in music with
chromatic progressions and extensive
modulations. He described a series of tunings where
enharmonic notes had the same pitch: in other words, the same note was used as both (say) E and D, thereby "bringing the keyboard into the form of a circle". This refers to the fact that the notes or keys may be arranged in a
circle of fifths and it is possible to modulate from one key to another without restriction. This is also the source of the terms "circular temperament" or "circulating temperament". Although
equal temperament is discussed by Werckmeister in his treatises, it is distinguished from non-equal well temperaments. ==Forms==