First off, bravo PeterT! A wonderfully easy-to-follow introduction to modes.

Second, a question: how does this apply to the question of well-tempering? Before pianos were well-tempered, I assume starting on D and ending on D would NOT end up with a Doric scale, am I right?

Third, a mnemonic device:

Take PeterT's wonderful chart:

Ionian goes: W-W-H-W-W-W-H (all natural)
Dorian goes: W-H-W-W-W-H-W (b3, b7)
Phrygian goes: H-W-W-W-H-W-W (b2, b3, b6, b7)
Lydian goes: W-W-W-H-W-W-H (#4)
Mixolydian goes: W-W-H-W-W-H-W (b7)
Aeolian goes: W-H-W-W-H-W-W (b3, b6, b7)
Locrian goes: H-W-W-H-W-W-W (b2, b3, b5, b6, b7)

But order it in the order of added sharps or flats (using Ionian as a baseline):

Lydian (#4)
Ionian (all natural)
Mixolydian (b7)
Dorian (b3, b7)
Aeolian (b3, b6, b7)
Phrygian (b2, b3, b6, b7)
Locrian (b2, b3, b5, b6, b7)

Then add back in the letter each scale starts with when playing on the white keys:

F Lydian (#4)
C Ionian (all natural)
G Mixolydian (b7)
D Dorian (b3, b7)
A Aeolian (b3, b6, b7)
E Phrygian (b2, b3, b6, b7)
B Locrian (b2, b3, b5, b6, b7)

Well looky there! It's our old friend the circle of fifths! "Father Charles Goes Down And Ends Battle"

Maybe I'm the only one who thinks this is cool. But I think this is cool!

Tomorrow, I will show why this predicts UFO sightings in 1953 and Jesus Christ returning in late 2004. ;-)

Alex