later, a complete range of anything. The hexachordal system also distinguished between B (fa in the F hexachord, and known as "B molle" for 'soft B') and B♮ (mi in the G hexachord, and known as "B durum" for 'hard B'). Over time, the soft and hard variants of 'b' were depicted as a rounded '' and a squared-off '' which gradually developed into the modern flat and natural signs (or, in Northern Europe, into the letters 'b' and 'h'). Since a single hexachord did not cover every possible note in the range of the gamut (only C–A, F–D excluding B, or G–E excluding B), singers would have to "mutate" between hexachords if the range of a sixth was exceeded or if there was an alternation between B and B. In this way the "Guidonian" system of multiple hexachords was different from the modern system of solfège, wherein a single set of syllables suffices to name all possible pitches (including, often, chromatic pitches) within a mode. Because it included B durum, the G hexachord was called hexachordum durum; likewise, the F hexachord was called hexachordum molle. The C hexachord, containing neither B, was called hexachordum naturale. In the 14th century, this system was expanded to hexachords that would accommodate an increased use of signed accidentals. From this time onward, the use of such notes was called musica ficta. See also Diatonic hexachord References Further reading Claude V. Palisca. "Guido of Arezzo", Grove Music Online, ed. L. Macy (accessed June 13, 2007), grovemusic.com (subscription access). Andrew Hughes. "Solmization", Grove Music Online, ed. L. Macy (accessed March 12, 2006), grovemusic.com (subscription access). External links Margo Schulter, Hexachords, solmization, and musica ficta Music mnemonics Musical notation Medieval music theory