The name of the modes are proper nouns, and ought to be capitalized. I also added a little more background behind the cycle of the tones.
The current usage of Byzantine
chant is built upon eight modes (tones), each mode with its own specific tonality. The modes change sequentially from week to week, starting the Monday after the [[Sunday of St. Thomas]], with mode 1. Within [[Bright Week]] itself, the mode changes each day, thus: :Sunday – mode 1, :Monday – mode 2, :Tuesday – mode 3, :Wednesday – mode 4, :Thursday – mode plagal of the first (5), :Friday – mode plagal of the second (6), :Saturday – mode plagal of the fourth (8).
grave mode (7) was chosen as the mode to be left out due to its heavier sound, considered least appropriate for the festal period among the eight modes. Since [[Pentecost]] falls on the Sunday when the grave mode would have been used in the normal sequence, the mode is once again skipped and the hymns of Pentecost are used. The sequence resumes the following week with plagal of the fourth.
In the time between a [[Great Feasts|great feast]] and its [[Leavetaking|leave-taking]], for example, during the week following Pentecost, the hymns of the feast are chanted rather than the hymns pertaining to the mode of the week.