Hi all,
Many years ago, an explanation of the modes of the Major scale was presented to me which gave me a lightbulb moment - it was concise and obvious, and presented in a format that I was already comfortable with (notated as a series of almost identical scales on a stave, in the order of light to dark sounding).
I thought it would be quite simple to present that in tidal syntax, and for anyone who's been grappling with the concept of modes, this might be a way for me to impart a lightbulb moment for you too.
Consider the Major Scale, in tidal syntax:
d1 $ note "0 2 4 5 7 9 11 12"
# s "superpiano"
-- 12 is the same note as 0, an octave higher
The Modes of the Major scale are derived by taking the pattern of Whole Tone and Half tone (Semitone) steps between each note, and shifting the starting step by one - so that pattern could be represented as:
0 2 4 5 7 9 11 12
W W H W W W H
Shift it by one, so we start on the second step instead and we get:
W H W W W H W
d1 $ note "0 2 3 5 7 9 10 12"
# s "superpiano"
It changes the tonality (how light or dark) the scale sounds significantly - in this case, it's much darker!
The modes can be arranged in order from light to dark, and in this order each mode changes by one semitone. In tidal syntax:
Light to Dark
(Major modes)
-- Lydian
-- this has a sharp 4th relative to the regular Major scale
d1 $ note "0 2 4 6 7 9 11"
# s "superpiano"
-- Ionian (or our regular Major scale)
-- 6 -> 5 relative to Lydian, ie natural 4th
d1 $ note "0 2 4 5 7 9 11"
# s "superpiano"
-- Mixolydian
-- 11 -> 10 relative to Ionian, ie flatted or "dominant" 7th
d1 $ note "0 2 4 5 7 9 10"
# s "superpiano"
(minor modes)
-- Dorian
-- 4 -> 3 relative to Mixo, ie flatted or "minor" 3rd
d1 $ note "0 2 3 5 7 9 10"
# s "superpiano"
-- Aeolian
-- 9 -> 8 relative to Dorian, ie flatted 6th
d1 $ note "0 2 3 5 7 8 10"
# s "superpiano"
-- Phrygian
-- 2 -> 1 relative to Aeolian, ie flatted 2nd
d1 $ note "0 1 3 5 7 8 10"
# s "superpiano"
-- Locrian
-- 7 -> 6 relative to Phrygian, ie flatted or "diminished" 5th
d1 $ note "0 1 3 5 6 8 10"
# s "superpiano"
Fortunately, you don't need to remember the exact patterns to use them in tidal, you get handy shortcuts!
d1 $ note (scale "lydian" "0 1 2 3 4 5 6 7")
# s "superpiano"
d1 $ note (scale "ionian" "0 1 2 3 4 5 6 7")
# s "superpiano"
d1 $ note (scale "mixolydian" "0 1 2 3 4 5 6 7")
# s "superpiano"
d1 $ note (scale "dorian" "0 1 2 3 4 5 6 7")
# s "superpiano"
d1 $ note (scale "aeolian" "0 1 2 3 4 5 6 7")
# s "superpiano"
d1 $ note (scale "phrygian" "0 1 2 3 4 5 6 7")
# s "superpiano"
d1 $ note (scale "locrian" "0 1 2 3 4 5 6 7")
# s "superpiano"
So hopefully having an idea of the Lightness/Brightness or darkness of the mode will be able to help you choose a set of notes that will fit your piece more accurately than simply guessing, or making lots of off-by-one errors like me 
go to two octaves, and you should have all the notes you need for some beautiful diatonic melodies:
d1 $ note (scale "ionian" "0 1 2 3 4 5 6 7 8 9 10 11 12 13 14")
# s "superpiano"
