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,
Octave (poetry) Octave (poetry) An octave is a verse form consisting of eight lines of iambic pentameter (in English) or of hendecasyllables (in Italian). The most common rhyme scheme for an octave is "abba abba". An octave is the first part of a Petrarchan sonnet, which ends with a contrasting sestet. In traditional Italian sonnets the octave always ends with a conclusion of one idea, giving way to another idea in the sestet. Some English sonnets break that rule, often to striking effect. In Milton's Sonnet 16, the sestet begins early, halfway through the last line of the octave: Patience's too-quick reply