I was just wondering if anything is particularly communicated by which tones received which traditional gregorian numbers. For instances, is Tone I "tone *one*" because it was the most well known, or original, or oldest? Likewise, Tone Two might be the next oldest, and Tone 8, in the early middle ages, was the newest? Likewise with the endings: Is the "first" ending thus called because it is the most well-known and familiar -- the first to be taught and commended?
No, the numbering follows the final (tonic) and ambitus (range) of the mode and goes sequentially: I & II have a final on re/D (or la/A if transposed), III & IV on mi/E, V & VI on fa/F (do/C if transposed), and VII & VIII on sol/G. The odd-numbered modes have an ambitus spanning an octave above the final; the even, an octave from the fourth below the final to the fifth above. As for the endings of the psalm tones, that depends on what best suits the antiphon. The letter next the psalm tone indicates the termination, capitalized if also the final of the mode. Mode I does seem to be the most common, but none of the eight theoretical chant modes ends on la, ti, or do unless transposed, so re is the logical starting point. For the Gloria Patri tones, I believe the alternative Euouae endings are given from most to least common, but maybe someone here knows better.
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