Editing Hexachord (section)

==Middle Ages==
{{Main|Guidonian hand#The hexachord in the Middle Ages}}
The hexachord as a mnemonic device was first described by [[Guido of Arezzo]], in his ''Epistola de ignoto cantu''.<ref>Guido d'Arezzo, "Epistola de ignotu cantu [ca. 1030]", abridged translation by Oliver Strink in ''Source Readings in Music History'', selected and annotated by Oliver Strunk, 5 vols. (New York: W. W. Norton, 1965): 1:121–25. Latin test in Martin Gerbert, ''Scriptores ecclesistici de musica sacra potissimum'', 3 vols. (St. Blasien, 1784), 2:43–46, 50. See also Clause V. Palisca, "Introduction" to Guido's ''Micrologus'', in ''Hucbald, Guido, and John on Music: Three Medieval Treatises'', translated by Warren Babb, edited, with introductions by Claude V. Palisca, index of chants by Alejandro Enrique Planchart, 49–56, Music Theory Translation Series 3 (New Haven and London: Yale University Press, 1978): esp. 49–50. {{ISBN|0-300-02040-6}}.</ref> In each hexachord, all adjacent pitches are a [[whole tone]] apart, except for the middle two, which are separated by a [[semitone]]. These six pitches are named ''ut'', ''re'', ''mi'', ''fa'', ''sol'', and ''la'', with the semitone between ''mi'' and ''fa''. These six names are derived from the first syllable of each half-verse of the first stanza of the 8th-century Vesper hymn [[Ut queant laxis|''Ut'' queant laxis ''re''sonare fibris / ''Mi''ra gestorum ''fa''muli tuorum]], etc.<ref>Guido d'Arezzo, "Epistola de ignotu cantu [ca. 1030]", abridged translation by Oliver Strink in ''Source Readings in Music History'', selected and annotated by Oliver Strunk, 5 vols. (New York: W. W. Norton, 1965): 1:121–25. Citation on p. 124.</ref> Melodies with a range wider than a major sixth required the device of mutation to a new hexachord. For example, the hexachord beginning on C and rising to A, named ''hexachordum naturale'', has its only semitone between the notes E and F, and stops short of the note B or B{{Music|flat}}. A melody moving a semitone higher than ''la'' (namely, from A to the B{{Music|flat}} above) required changing the ''la'' to ''mi'', so that the required B{{Music|flat}} becomes ''fa''. Because B{{Music|flat}} was named by the "soft" or rounded letter B, the hexachord with this note in it was called the ''hexachordum molle'' (soft hexachord). Similarly, the hexachord with ''mi'' and ''fa'' expressed by the notes B{{Music|natural}} and C was called the ''hexachordum durum'' (hard hexachord), because the B{{Music|natural}} was represented by a squared-off, or "hard" B. Starting in the 14th century, these three hexachords were extended in order to accommodate the increasing use of signed accidentals on other notes.<ref name="Jehoash Hirshberg 2001">Jehoash Hirshberg, "Hexachord", ''The New Grove Dictionary of Music and Musicians'', second edition, edited by [[Stanley Sadie]] and [[John Tyrrell (professor of music)|John Tyrrell]] (London: Macmillan Publishers, 2001).</ref>

The introduction of these new notes was principally a product of [[polyphony]], which required the placing of a [[perfect fifth]] not only above the old note B{{Music|natural}}, but also below its newly created variant, this entailing, as a result of the "original sin" committed by the well-meant innovation B{{Music|flat}}, the introduction of the still newer respective notes F{{Music|sharp}} and E{{Music|flat}}, with as consequences of these last C{{Music|sharp}} and A{{Music|flat}}, and so on. The new notes, being outside the [[Gamut (music)|gamut]] of those ordinarily available, had to be "imagined", or "feigned" (it was long forbidden to write them), and for this reason music containing them was called ''[[musica ficta]]'' or ''musica falsa''.<ref>Andrew Hughes and Edith Gerson-Kiwi, "Solmization [solfatio, solmifatio]", ''The New Grove Dictionary of Music and Musicians'', second edition, edited by [[Stanley Sadie]] and [[John Tyrrell (professor of music)|John Tyrrell]] (London: Macmillan Publishers, 2001): §4, "Expansion of the Hexachord System".</ref>