Key signatures for different modes?

I want to write a song using the Aeolian mode. How should I go about choosing my key signature once I pick my tonic note?

Aeolian mode is easy, because it conforms to the standard minor key signature for any tonic.

Example:

For A, no key signature.

For C, three flats (B-flat, E-flat, A-flat).

For F, four flats (the above and D-flat).

For E, one sharp (F-sharp).

It works for any tonic.

In other modes, it's not always so simple. You have to figure out which chromatics (black-keys) are involved in the mode on a given tonic, and figure it in from there. Sometimes there's no way to do it cleanly with a key signature, and you just have to add accidentals as needed.

Hope that helps.

oh, alright, thank you! It's so simple :)

oh, alright, thank you! It's so simple :)

Yeah, you picked an easy one! Thank God for small favours. :D

I remember Bartok used some funky ones where it said C#, but no F# in the key signature. Think it was the Mikrokosmos

Yasamune, I'm not familiar with Mikrokosmos. What is the tonic in the mode Bartok used? Since Bartok was very much in tune with (and influenced by) the folk-music traditions of his native Hungary, it could be he was trying to emulate one of the folk-modes he was familiar with, which may or may not conform to the classic Greek modes.

Nor am I Graham. I just remember I took a look at one and there was a C# sitting in the key signature with nothing else. I assume Bartok knew what he was doing cause I sure don't and am way too lazy right now to try and say otherwise :P

That is the key signature of D melodic Minor...

True, if the tonic is D. Knowing Bartok even as little as I do, though, the chances are good that his tonic is F or something.

*makes mental note to look up Mikrokosmos*

So that would be Lydian #5... so? It could be any MODE from the SCALE D Melodic Minor. No need to be afraid of it.

Yes, but the tonic being F, for example, has its own harmonic ramifications:

There is no standard key signature to denote this mode - either it has to have only a C#, or no key signature at all with accidentals.

Yes.... and the problem?

No matter what 'tonic' is perceived, and how you notate it, the source scale is the same

Then I apparently don't understand what modes really are.

* makes mental note to study more on the subject *

Honestly, I thought the tonic had everything to do with it.

If you want to compose in, say, F# Phrygian, just use the key signature for the relative major (DMaj in this case). I would also add the text Phrygian just above the staff at the beginning.

A mode is a scale derived from another scale by shifting the tonic. For example: The dorian mode is derived from the ionic scale by starting on the second degree. The Lydian #5 is a mode derived from the melodic minor by starting on the third degree.