the scales that gregorian chants were derived from
Gregorian chant Early plainchant, like much of Western music, is believed to have been distinguished by the use of the diatonic scale. Modal theory, which postdates the composition of the core chant repertory, arises from a synthesis of two very different traditions: the speculative tradition of numerical ratios and species inherited from ancient Greece and a second tradition rooted in the practical art of cantus. The earliest writings that deal with both theory and practice include the Enchiriadis group of treatises, which circulated in the late ninth century and possibly have their roots in an earlier, oral tradition. In contrast to the ancient Greek system of tetrachords (a collection of four continuous notes) that descend by two tones and a semitone, the Enchiriadis writings base their tone-system on a tetrachord that corresponds to the four finals of chant, D, E, F, and G. The disjunct tetrachords in the Enchiriadis system have been the subject of much speculation, because they do not correspond to the diatonic framework that became the standard Medieval scale (for example, there is a high F#, a note not recognized by later Medieval writers). A diatonic scale with a chromatically alterable b/b-flat was first described by Hucbald, who adopted the tetrachord of the finals (D, E, F, G) and constructed the rest of the system following the model of the Greek Greater and Lesser Perfect Systems. These were the first steps in forging a theoretical tradition that corresponded to chant.
Latin Mass A further distancing between the concepts of "Tridentine Mass" and "Latin Mass" was brought about by the 1964 Instruction on implementing the Constitution on Sacred Liturgy of the Second Vatican Council, which laid down that "normally the epistle and gospel from the Mass of the day shall be read in the vernacular". Episcopal conferences were to decide, with the consent of the Holy See, what other parts, if any, of the Mass were to be celebrated in the vernacular.[3] Permissions were thus granted from 1967 onwards to celebrate most of the Tridentine Mass in vernacular languages, including the Canon.