Lydian mode has half steps between 4-5 and 7-8.
Mixolydian mode has half steps between 3-4 and 6-7.
Aeolian mode (presently the natural minor scale) has half steps between 2-3 and 5-6.
Locrian mode has half steps between 1-2 and 4-5.
APPENDIX 4
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Gregory the Great, the first great pope of the Middle Ages, solidified papal power (c. 590–604). He is credited with composing
much of the music used in the Roman liturgy, resulting in the label “Gregorian chant.” It is more likely that Pope Gregory codified
these chants, rather than composing them. To the original four modes described by St. Ambrose, the fourth century theorist, Pope
Gregory added four others.
Historical note