Musica ficta (from Latin, "false", "feigned", or "fictitious" music) was a term used in European music theory from the late 12th century to about 1600 to describe pitches, whether notated or added at the time of performance, that lie outside the system of musica recta or musica vera ("correct" or "true" music) as defined by the hexachord system of Guido of Arezzo. Modern use Today, the term is often loosely applied to all unnotated inflections (whether they are actually recta or ficta notes; see below) that must be inferred from the musical context and added either by an editor or by performers themselves. However, some of the words used in modern reference books to represent musica ficta, such as "inflection", "alteration", and "added accidentals" lie outside the way many Medieval and Renaissance theorists described the term. Historical sense and relation to hexachords Throughout the period that incorporated musica ficta, singers sight read melodies through a series of interlocked hexachords that formed the backbone of the solmization system—a method that eventually became the modern system of tonic solfa. To sing notes outside the recta pitches of the gamut (the range generally available to composers and performers, i.e., from G at the bottom of the modern bass clef to E at the top of the treble clef), performers had to invoke "fictive" hexachords to sing pitches such as F or E. Hexachords normally were formed only on C, F, and G, and the interval pattern within each of these hexachords was always tone-tone-semitone-tone-tone, which was sung as ut re mi fa sol la. Hence, if singers needed to sing the pitch F, they had to think of the half step between F and G as the solmization syllables mi and fa, for mi-fa always represented the half step within a hexachord. When they did this, they invoked a nominal hexachord starting on the note D, and this hexachord was considered fictive because it contained a false or fictitious F (that is, a pitch that did not belong to the recta notes of the gamut). Moreover, since the hexachord built on F naturally contained a B, music based on a scale involving the soft or F hexachord had the pitch B as part of the recta notes of the scale. However, in the 16th century, the signs used to represent these fictive notes (the signs for b mollis [] and b durum [])