Seventh chord an augmented fifth, and an augmented seventh (i.e., a sequence of 3 major thirds, such as C–E–G–B), is a rarely used tertian seventh chord. The reason is that the augmented seventh interval is enharmonically equivalent to one entire octave (in equal temperament, 3 major thirds = 12 semitones = 1 octave) and is hence perfectly consonant with the chord root. The seven commonly used chords are: Seventh chords can also be constructed using augmented or diminished thirds. These chords are not tertian and can be used in non-tertian harmony. There are many (mathematically, 64) chords that can be built, however,
Sicilian octave Renaissance and has seldom been used in English except as an illustration of the form. Before the 15th century, however, it was used often by poets in southern Italy, and was an important influence for Petrarch in his sonnets. Boccaccio, who popularized and may have invented the unrelated ottava rima, used the Sicilian octave a total of once, in his early romance Filocolo. The epitaph of Giulia Topazia is a Sicilian octave: Sicilian octave The Sicilian octave (Italian: "ottava siciliana" or "ottava napoletana", lit. "Neapolitan octave") is a verse form consisting of eight lines of eleven syllables each, called a