# Augmented seventh

In classical music from Western culture, an **augmented seventh** is an interval produced by widening a major seventh by a chromatic semitone. For instance, the interval from C to B is a major seventh, eleven semitones wide, and both the intervals from C♭ to B, and from C to B♯ are augmented sevenths, spanning twelve semitones. Being augmented, it is classified as a dissonant interval.[4] However, it is enharmonically equivalent to the perfect octave.

Inverse | diminished second |
---|---|

Name | |

Other names | - |

Abbreviation | A7[1] |

Size | |

Semitones | 12 |

Interval class | 0 |

Just interval | 125:64[2][3] or 2025:1024[3] |

Cents | |

Equal temperament | 1200[3] |

24 equal temperament | 1150 |

Just intonation | 1159[3] or 1180[3] |

Since an octave can be described as a major seventh augmented by a diatonic semitone, the augmented seventh is the sum of an octave, plus the difference between the chromatic and diatonic semitones, which makes it a highly variable quantity between one meantone tuning and the next. In standard equal temperament, in fact, it is identical to the perfect octave (

In just intonation, three major thirds in succession make up an augmented seventh, which is just short of an octave by 41.05 cents. Adding a diesis to this makes up an octave. Hence, this interval's complement, the diminished second, is often referred to as a diesis.

## See also

## Sources

- Benward & Saker (2003).
*Music: In Theory and Practice, Vol. I*, p.54. ISBN 978-0-07-294262-0. Specific example of an A7 not given but general example of major intervals described. - Haluska, Jan (2003).
*The Mathematical Theory of Tone Systems*, p.xxvi. ISBN 0-8247-4714-3. Classic augmented seventh. - Duffin, Ross W. (2008).
*How equal temperament ruined harmony : (and why you should care)*(First published as a Norton paperback. ed.). New York: W. W. Norton. p. 163. ISBN 978-0-393-33420-3. Retrieved 28 June 2017. - Benward & Saker (2003), p.92.