What is a key signature for writing in modes other than major and minor?

Question

I have trouble deciding what accidentals to put in the key signature for pieces in Dorian, Phrygian, Lydian or Mixolydian modes. Is there any kind of convention to follow?

Answer 1

Yes, the convention you would follow would be to use the key signature from the related major scale. For example, if your piece was in C Lydian, the related major scale would be G major. So, you would write the key signature for Gmajor, i.e., one sharp (F#).

Answer 2

Just a state of mind!! Lets look at good old C major no sharp no flats. If I saw that in a key signature and I looked at the melody or chord progression based on d e f g a b c d, I would know I'm in Dorian in D.

I don't play like my aunt lulu

Ionan Dorian Phrygian.....

Ionian is a major scale, a scale starting at the second degree of a major scale is in dorian so looking at B flat major the second degree will be C giving C dorian: c d eb f g a Bb c and so on.