In order to gain an ut at the bottom on which to begin the first set of voces, Guido placed a G below
the A that normally marked the lower end of the modal system. This extra G was represented by its Greek
equivalent, gamma. Its full name within the array of voces was “Gamma ut,” which (shortened to gamut)
became the name of the array itself. (The word “gamut,” of course, has entered the common English
vocabulary to denote the full range of anything.) The two versions of B (the one sung as mi over G,
corresponding to our B natural, and the one sung as fa over F, corresponding to B-flat), were assigned to a
single mutable space, whose actual pitch realization would depend on the context. The higher B was
known as the hard one (durus), and was represented by a square-shaped letter that eventually evolved
into the modern natural sign. The hexachord containing it was also known as the “hard” hexachord
(hexachordum durum). The lower one, which softened augmented fourths into perfect ones, was known
accordingly as soft (mollis) and was represented by a rounded letter that eventually evolved into the
modern flat sign. The hexachord containing B-flat (B-mollis) was known as the “soft” hexachord
(hexachordum molle; the original module, derived from the hymn, was called the “natural” hexachord.)
Eventually, the use to which Guido put the C–A hexachord module, and the concepts that arose from it,
began to influence the more theoretical notion of the hexachord as expounded by Hermann. One now could
distinguish pieces ending “on ut” (Regina caeli, for example) from pieces ending “on re” (like Salve
Regina). A whole intervalspecies could be summoned up by a single syllable. This, too, reinforced the
tendency to simplify the concept of mode and reduce it all the more to our familiar major-minor dualism.
Eventually the “ut” modes (like G with a B natural) were called durus, and “re” modes (like G with a B
flat, a “transposed” Dorian) were called mollis. This terminology survives to this day in some languages,
like German and Russian, as equivalents for major and minor (thus in German G-dur means “G major”
and g-moll means “G minor.”) In French and Russian, the word bémol (from “B-mollis”) denotes the flat
sign.
As an aid toward internalizing the whole set of voces and applying them to the actual notes written on
Guido’s other invention, the staff, Guido—or, more likely, later theorists acting in his name—adopted a
mnemonic device long used by calendar makers and public speakers, whereby items to be memorized
were mapped spiralwise onto the joints of the left palm (Fig. 3-6). (The once widespread use of such
devices is still reflected in our daily language by expressions like “rule of thumb” and “at one’s
fingertips.”) In its fully developed musical form (not actually reached until the thirteenth century, two
hundred years after Guido), each location on the “Guidonian hand” (and one in space, above the middle
finger) represented a musical locus, defined by the conjunction of two overlapping cycles: the octave-
cycle naming the notes as written (the claves, or letter names), and the series of hexachord placements that
assigned voces to each of the claves. A specific locus, then, represents the product of a clavis and a vox.
C fa ut (lowest joint of index finger), for example, is the C below middle C (C), and only that C: it can be
solmized only in the hard hexachord (in which it is fa) and the natural (in which it is ut); there is no F
below it in the gamut, so it cannot be solmized as sol. Middle C (c, top joint of ring finger) is C sol fa ut:
it can be solmized in all three hexachords. The C above middle C (cc, second joint of ring finger), and
only that C, is C sol fa, for it can only be solmized in the soft and hard hexachords. To sing it as ut would
imply that the gamut (or “hand,” as it was fondly called) continued past its upper limit.