Editing Augmented sixth chord (section)

===Standard function===
From the [[Baroque music|Baroque]] to the [[Romantic music|Romantic periods]], augmented sixth chords had the same [[Diatonic function#Diatonic functions of notes and chords|harmonic function]]: as a [[chromatic]]ally altered [[predominant chord]] (typically, an alteration of [[supertonic|ii{{su|b=3|p=4}}]], [[subdominant|IV{{su|b=5|p=6}}]], [[submediant|vi<sup>7</sup>]] or their [[Parallel key|parallel]] equivalents in the minor mode) leading to a dominant chord. This movement to the dominant is heightened by the [[semitone|semitonal]] resolution to {{music|scale|5}} from above and below (from {{music|flat}}{{music|scale|6}} and {{music|sharp}}{{music|scale|4}});<ref>{{cite book |last1=Kostka |first1=Stefan |first2=Dorothy |last2=Payne |year=1995 |title=Tonal Harmony |edition=3rd |place=New York, NY |publisher=McGraw Hill |page=384 |ISBN=0070358745 }}</ref> essentially, these two notes act as [[leading-tone]]s.

During the Baroque and early Classical periods, for instruments tuned to [[meantone]] systems rather than [[well temperament]]s, the augmented sixth note ({{sup|{{music|#}}}}6) produced an excellent approximation to a [[harmonic seventh]]. The match is particularly close in [[quarter comma meantone]], where {{sup|{{music|#}}}}6 is only 3&nbsp;[[cents (music)|cents]] flat from H{{sub|7}}. This made a major triad with an added {{sup|{{music|#}}}}6 a fully consonant / harmonic chord (harmonics&nbsp;4, 5, 6, 7); as opposed to a modern [[12 tone equal temperament|equal tempered]] [[dominant seventh chord]] (M add{{sup|{{music|b}}}}7) which misses being harmonic with the minor&nbsp;7th pitch 31&nbsp;cents sharp – a dissonance.

This characteristic has led many analysts<ref name=Piston419>{{cite book | last1 = Piston | first1 = Walter | author1-link = Walter Piston | first2 = Mark | last2 = de Voto | year = 1987 | title = Harmony | edition = 5 | location = New York, NY | publisher = [[W. W. Norton & Company, Inc.]] | isbn = 0-393-95480-3 | page = 419 | ref = CITEREFPiston419 }}</ref> to compare the voice leading of augmented sixth chords to the [[secondary dominant]] V of V because of the presence of {{music|sharp}}{{music|scale|4}}, the leading-tone of V, in both chords. In the [[major mode]], the chromatic voice leading is more pronounced because of the presence of two chromatically altered notes, {{music|flat}}{{music|scale|6}} and {{music|sharp}}{{music|scale|4}}, rather than just {{music|sharp}}{{music|scale|4}}.

In most occasions, the augmented-sixth chords precede either the dominant, or the [[tonic (music)|tonic]] in [[second inversion]].{{sfn|Rimsky-Korsakov|1924|p=121}} The augmented sixths can be treated as chromatically altered [[Passing chord|passing chords]].{{sfn|Rimsky-Korsakov|1924|p=121}}