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,
Short octave The actual note assignments can be seen in the following diagram: It can be seen that only two notes of the chromatic scale, C and D, are missing. An analogous arrangement existed for keyboards with G instead of C at the bottom. According to Trevor Pinnock, the short octave is characteristic of instruments of the 16th century. He adds, "in the second half of the 17th century, when more accidentals were required in the bass, 'broken octave' was often used." The short/broken octave principle not only survived, but was even developed further in one particular location, namely Vienna. The "Viennese