Editing Diatonic scale (section)

===Middle Ages===
The scales corresponding to the medieval [[church modes]] were diatonic. Depending on which of the seven notes of the diatonic scale you use as the beginning, the positions of the intervals fall at different distances from the starting tone (the "reference note"), producing seven different scales. One of these, the [[Locrian mode|one starting on B]], has no pure fifth above its reference note (B–F is a [[diminished fifth]]): it is probably for this reason that it was not used. Of the six remaining scales, two were described as corresponding to two others with a B{{music|b}} instead of a B{{music|natural}}:

# A–B–C–D–E–F–G–A was described as D–E–F–G–A–B{{music|b}}–C–D (the modern [[Aeolian mode]]s whose reference notes are A and D, respectively, corresponding to the [[Aeolian mode]]s of [[C major]] and [[F major]], respectively)
# C–D–E–F–G–A–B–C was described as F–G–A–B{{music|b}}–C–D–E–F (the modern [[Ionian mode]]s whose reference notes are C and F, respectively, corresponding to the [[Ionian mode]]s of [[C major]] and [[F major]], respectively).

As a result, medieval theory described the church modes as corresponding to four diatonic scales only (two of which had the variable B{{music|natural}}/{{music|b}}). They were the modern [[Dorian mode|Dorian]], [[Phrygian mode|Phrygian]], [[Lydian mode|Lydian]], and [[Mixolydian mode|Mixolydian]] modes of [[C major]], plus the [[Aeolian mode|Aeolian]] and [[Ionian mode|Ionian]] modes of [[F major]] when B{{music|b}} was substituted into the Dorian and Lydian modes of [[C major]], respectively.