Research on traditional modes from Eric Taylor’s “AB Guide to Music Theory-Part II” has given me a greater outline about what these are and how they paved the way for more widely known scalic formats that are used today.
Thinking away from the normal major/minor scales makes this subject easier to understand. Historically, modes existed around unaccompanied melodies; folk songs were used to be based upon these unaccompanied melodies.
What is a mode? For every white note on a keyboard, we can play a scale from it and only using white notes. Depending on which white note we start on will determine the name of the mode.
And to add a little more confusion to the mix, we have two different modes; authentic and plagal.
“Authentic Mode” = this always starts from the first or “final” note (as opposed to the “tonic” note. Yes, it’s confusing!)
“Plagal Mode” = this starts a perfect 5th/perfect 4th below the first note; prefixed with the word “Hypo” which is Greek for “under”.
Ionian: C to C
Dorian: D to D
Phrygian: E to E
Lydian: F to F
Mixolydian: G to G
Aeolian: A to A
Melodies in every mode have their own patterns that characterise each of them, short cells of note patterns that can be combined; notes within them can then be used in any order. Not all notes within a mode are used sometimes, which can imply a pentatonic scale if gaps are formed.
Common pentatonic folksongs are “Auld Lang Syne” and “Old MacDonald”. Of course, plainsong and secular folksongs were around before any methods of writing down music had been established. These were usually sung at a convenient pitch. Notation then showed the intervals against the notes.
When fixed instruments came into being like the organ, notation implied the pitch precisely, which didn’t appeal to some composers who didn’t want their music at these exact pitches. And so some 16th century composers like Palestrina got round this by transposing their music up a perfect 4th with the addition on a B-flat as a key signature.