A Dictionary of Music and Musicians/Perfect
PERFECT. Of Cadences the word 'perfect' is used to indicate such as give the most absolute effect of a conclusion, by passing through a chord or chords which are highly characteristic of a key to the tonic chord of that key in its first position. [See Cadence.] Of Intervals the word is chiefly used in modern times to describe certain of the purest and simplest kinds, as fifths and fourths, when in their most consonant forms; in the early days of modern music it was used in contrast to the terms 'imperfect' and 'middle' to classify the consonances in the order of their theoretical excellence. [See Harmony, Interval, Temperament].
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