Editing Perfect fourth (section)

===Middle Ages===
In [[medieval music]], the [[tonality]] of the common practice period had not yet developed, and many examples may be found with harmonic structures that are built on fourths and fifths. The ''[[Musica enchiriadis]]'' of the mid-10th century, a guidebook for musical practice of the time, described singing in parallel fourths, fifths, and octaves. This development continued, and the music of the [[Notre Dame school]] may be considered the apex of a coherent harmony in this style.

[[Image:AveMarisStellaDufay.png|thumb|left|400px|Fourths in Guillaume Du Fay's Antiphon ''Ave Maris Stella'']]
For instance, in one "Alleluia" ([[Image:Loudspeaker.svg|11px]][//upload.wikimedia.org/wikipedia/commons/3/34/Perotin_Alleluya_Quarten_for_wikipedia.mid Listen]) by [[Pérotin]], the fourth is favoured. Elsewhere, in parallel ''[[organum]]'' at the fourth, the upper line would be accompanied a fourth below. Also important was the practice of ''[[Fauxbourdon]]'', which is a three-voice technique (not infrequently [[Improvisation (music)|improvisatory]]) in which the two lower voices proceed parallel to the upper voice at a fourth and sixth below. ''Fauxbourdon'', while making extensive use of fourths, is also an important step towards the later triadic harmony of tonality, as it may be seen as a [[first inversion]] (or 6/3) triad.

This parallel 6/3 triad was incorporated into the contrapuntal style at the time, in which parallel fourths were sometimes considered problematic, and written around with ornaments or other modifications to the ''Fauxbourdon'' style. An example of this is the start of the Marian-[[Antiphon]] ''Ave Maris Stella'' ([[Image:Loudspeaker.svg|11px]][//upload.wikimedia.org/wikipedia/commons/3/3d/AveMarisStellaDufay_for_wikipedia.mid Listen]) by [[Guillaume Dufay]], a master of ''Fauxbourdon''.