I have trouble deciding what accidentals to put in the key signature for pieces in Dorian, Phrygian, Lydian or Mixolydian modes. There seem to be trade-offs associated with each choice.

For example, when writing in G Mixolydian, setting an empty key signature makes it look like C major or A minor. Having the F# in the key signature forces me to put accidentals all over the piece to mark F naturals.

I prefer to use (in this example) the key signature of G major and natural signs on every F, especially when writing for choir. Singers with varying reading skills will often unconsciously assume that if the piece has G as the tonic, then it is in G major. The natural sign on every F will help them remember there is something special about it.

Is there any kind of convention to follow?

  • 11
    The music itself should clarify any confusion about key signature. How do you distinguish between C-major and A-minor? By looking at the music: pieces in A-minor have their tonal center obviously at A rather than C. If your tonal center is clearly G but all the F's are naturals, then any musician will be able to tell that it's in G-mixolydian. May 25, 2011 at 16:35
  • Not an answer because someone should elaborate on it (damn, am I lazy), but look at the way jazz music is written in Real Books! There's no better examples of music changing tonal centers often. Miles Davis' "Tune up" as an example (page 437 of the Real Book 1) has an empty key signature and uses accidentals in a manner that is congenial to the key of the two of four bars to which the notes belong. Not a convention, but definitely an acquired best practice.
    – wizclown
    Jan 24, 2019 at 14:57

12 Answers 12


The convention generally follows that which we see for minor key signatures. There is not a 1 to 1 relationship of key signature to root, rather, the key signature is there to tell us what notes exist in the scale. Then, we use the music itself to figure out where the root is.

If you were writing in D phrygian, for example, would you have two sharps in the key signature and then naturalize all Fs and Cs while flatting the Bs and Es? I should hope not, that would be confusing as all heck as far as I'm concerned. You would write two flats and be done with it.

And yes, it's true, writing a natural key signature for G mixolydian could easily be confused for C major. OR for A minor. OR for F lydian, D dorian, or B locrian. We already have this convention for major and minor (i.e. Ionian and Aeolian), it's just that most people don't realize there are other possibilities. When they start seeing that in the music, they'll realize soon enough.


The "church modes" as we know them, are the ones with the most background in western tonality, so I consider this convention to apply primarily to them. When you're talking about scales like super locrian or lydian dominant, there exists far less precedent. These most commonly occur in jazz music, where the key signature (if any) is most likely going to be a simple representation of overall major or minor key. The key signature matters less in this situation, since the scale/mode is going to be changing with the chords every bar or so anyway.

Similarly, when you have scales that are less common in western common practice, like the Arabic scale, Ukrainian minor, what have you; there is little history of these being notated according to western traditional rules. In many cases the musical tradition would not be notated, or there would be an alternate system of notation.

In contrast, the common usage of modes like mixolydian or dorian would be in a harmonically inactive setting. This lends itself to using one key signature for the entirety of the piece. If you're trying to notate non-western-traditional music, feel free to make up your own rules, but if you're using these types of scales in a jazz or highly harmonically active context, your key signature is probably not going to be directly related (should it exist at all).

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    If I was writing in D phrygian, I would use a D minor key signature.
    – mathlander
    Nov 25, 2023 at 3:28

I've played a lot of Eastern European music and often the minor keys will show the mode in the key signature e.g G minor has F sharp and B flat in the key signature so no accidentals needed all over the place.

Another is a mode based on E that only has a G sharp in the key signature.

It may not be a familiar to a newer musician, but I find once people know about it, they're fine.

  • The mode based on E with a G sharp sounds like A harmonic minor, only based on E.
    – Gauthier
    May 26, 2011 at 6:02
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    Re: I wonder what notation programs can do it - I'm pretty sure Sibelius / Finale and those newer notation programs deal with it fine.
    – niggles
    May 26, 2011 at 6:24
  • Re: The mode based on E with a G sharp sounds like A harmonic minor - E is the dominant chord, A minor the 5th, but the major third pulls it strongly to E despite the rest of the normally sharp notes being lowered by a semitone. European music has some fun conventions like H = B and B = B flat when it comes to chords :-)
    – niggles
    May 26, 2011 at 6:27
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    To be more precise, the H and B convention of being B and Bb is in European countries with German based languages. Germany and Scandinavia, for example. In latin-European countries such as Italy and France, fixed-do is used and the notes are called do re mi fa sol la si/ti (according to wikipedia, that is the case "In the major Romance and Slavic languages"). I just wanted to point out that there are differences within Europe :)
    – Gauthier
    May 26, 2011 at 6:43

I appear to be the only one (with my quick viewing of this thread) that feels that you SHOULD have accidentals. If you're in D dorian, write as if it was D minor (aka one flat) and have B naturals as accidentals. That lets your performer know that you're in a D minor mode, and looking at accidentals clarifies it.

Because it's so easy to divide the modes into Major Modes and Minor Modes, I'd stick to the key signatures of either the Minor or Major key of your scale, with appropriate accidentals. Accidentals do not inherently mean "by accident", nor does a piece require a key signature to be in a key (oh gods Poulenc's Oboe Sonata?). Consistent accidentals give just as much information as a key signature, and sometimes more.

I think the main problem that previous posters had with using existing key signatures and accidentals, was that people used examples of Minor Modes with Major key signatures. That's just silly guys! :-P

And that's how -I- use modes when writing and when teaching.

  • 4
    D Dorian has no actual relationship to D Aeolian other than the tonic. D Dorian is effectively a "key" just as D Aeolian or "relative minor" is seen as a "minor key". If A Aeolian has the same key signature as C Major, so then it follows that D Dorian must have the same key signature as C Major.
    – MrYellow
    Jul 30, 2019 at 23:48
  • In Swedish traditional music, this is the most common way it's done. Most players don't seem to think in terms of modes at all, and if a fiddler tells you a tune is in Am you have no way of knowing ift the f's and g's are sharp or natural without hearing the tune. In my experience from often asking them about it (I am a harmonica player) they typically don't know themselves without going through the tune to see. Also, accidentals are common, so much so that it's not always obvious if e.g the sixths are major or minor by default.
    – EdvinW
    Oct 23, 2023 at 10:04

Seems to me the most practical way would be to write the mode name in there. Make it obvious.


A clef armature is not meant to represent a musical key or mode, but rather to simplify the music reading. Musicians have a physiological mechanical memory for each. In contemporary music, after the atonal, dodecafonic and serial schools, clef armatures are becoming deprecated.

For modal music, you should use the key signature/clef armature relative to a pure mode.

For example, two sharps for E dorian, two flats for Eb lydian and so on. In cases where you want a complex mode, you'll need to put the extra accidentals as they occur. For example, a C augmented mixolydian would have a B flat at the clef (for C mixolydian), then a G sharp along the score. This is the simplest way for the instrumentalist to read.

If you want your players to know the mode of your tune or passage (useful for guiding improvisation), you might write the scale down explicitly for reference.

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    The German and Dutch words do not have much to do with "armature"; they mean literally "foresign" or "foresymbol." I would also note that the French word "clef" (modern spelling clé) means "key."
    – phoog
    Jan 23, 2019 at 20:29
  • @phoog, You are right, I have removed the argument about nomenclature.
    – fde-capu
    Dec 18, 2019 at 18:07

Most music I've seen that uses modes other than major and minor just uses the key signature that requires the fewest accidentals, and I've seen people who try to read it run into both problems you mention. (I'm thinking of two different choir pieces in F# mixolydian: people thought the first one was in B major and sight-read the second one as if the key signature were actually F# major.)

I think the solution you prefer is fine, but the real solution would be to increase general awareness of modes besides major and minor. :)

  • Yes, that's another problem. When you come to that amount of sharps in the key signature, you don't really count them. I would just assume the tonality from the start of the piece, which is not good.
    – Gauthier
    May 26, 2011 at 6:00

When I was a beginning musician I wanted the key signature that told me what notes to play, with the fewest accidentals written in the line. When I got a little more advanced I realized that knowing the "real" key/mode is important for understanding harmonic properties. This matters if you need to know where your part is in the blend (e.g. am I on the 3rd? the 5th? are you going to make me look at the bass line to find out?) or if anybody is going to be improvising. In your example, it is the difference between people thinking the piece is in C and knowing that it is in some flavor of G (though not ionian).

So unless you are writing a line for a single voice/instrument that will not be accompanied in any way, I would notate it per mode and use the accidentals.

  • Monica -- your answer brought back memories. I remember playing pieces in middle school where there would be a pair of key changes (say from C-major to G-major and back) where in the 1-sharp section I didn't have a single F or F# written so I wondered why the composer bothered to change the key signature for me. It wasn't until later that I realized the wisdom of showing a player the surrounding key/mode. Apr 18, 2013 at 2:02
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    Yes, I wondered about that sort of thing too! Eventually I learned. :-) (While I learned to play music from a young age, I didn't actually learn any music theory until college -- at which point I realized how much I'd been missing out on.) Apr 18, 2013 at 2:06
  • I imagine the tuba players must have run across this often, since if you're usually just playing the bass of I, ii, IV, V then adding a sharp and switching to the dominant doesn't ever use the new sharpened 7th degree. Apr 18, 2013 at 2:14

It appears that there is no definitively correct answer, with various sources indicating different approaches. So I submit the following argument for the use of accidentals for D Dorian, G mixolydian etc. as pure opinion with no claim to authority.

The most important information to immediately glean from a key signature, it would seem to me, would be tonal center and general modal nature of the scale - major or minor, i.e. brighter or darker.

This coupled with the fact that when viewing a key signature, we almost always expect it to represent one of two possible tonal centers, each corresponding to a minor or major mode scale, I would suggest that using the standard key signature for the given tonic and mode (major or minor) would get the reader this information the fastest, and be most in line with our standard expectations.

For example, if the piece were in D Dorian, using a key signature corresponding to D minor (i.e. one B flat) would far more rapidly convey a tonal center of D and a minor modal nature, than would a key signature with no sharps or flats. Even though the D Dorian scale has none.

That the reader may at first assume the piece was in D natural minor rather than D Dorian is less important than at first assuming the piece will be in A minor or C major, as is likely for most of us, with no sharps or flats in the key signature.

Seeing B natural accidentals in the piece would then lead to a minor ;) and less immediately important refinement of that initial assessment, that the piece is in fact in Dorian rather than natural minor.

In the example mentioned above, namely D Phrygian (which would have a B and E flat in the scale), I certainly would not use two sharps, which would correspond to a standard D major key signature. Phrygian being a minor mode scale, I would use the standard key signature for D minor, i.e. one B flat. Actual E flat notes would then be indicated by accidentals.

Granted this method requires the use of some accidentals but not particularly excessively, and as mentioned elsewhere, accidentals themselves do convey information.

In summary for a piece with a given tonal center and in;

Ionian, Lydian or Mixolydian mode: These being major mode scales, I would use the standard key signature corresponding to a MAJOR scale for the tonic.

and for:

Aeolian, Locrian, Dorian or Phrygian mode: These being minor mode scales, I would use the standard key signature corresponding to a MINOR scale for the tonic.


great discussion!

Each key signature contains 7 notes, A-G, and therefore 7 modes; we can start on any one of the 7 notes within a key signature.

Therefore, each of those 7 modes should use that key signature, otherwise we're teaching and/or encouraging a huge misconception and factual inaccuracy around key.

F lydian is part of the exact same key signature as C ionian (major). Putting it as F major with a B natural is wrong. It's also a failure to understand the circle of 4ths and 5ths and/or Western key signature in general.

Each key signature contains 7 modes by default due to having 7 notes and the fact that you can start a piece of music on any of the 7. When we move our key signature up or down a 5th/4th to gain/lose a flat or sharp, we're moving all 7 notes and therefore all 7 modes.

The ionian and aeolian are 2 of 7. The major and minor vocabulary is very misleading!


Keep it simple ! Use the key signature of the 'mother key'.E.g. D Dorian would have no # or b, C Phrygian would be 4flats etc. No-one has mentioned the difference between , say, G Dorian and the Dorian of G - 2 different keys !


Just saw this discussion, and this site for that matter. Both very nice!

I always choose to write my music as much as possible to reflect the ideas that I have.

If I write a modal melody, I don't want to see any accidental sharps or flats, because there is nothing accidental about them (unless of course I construct a melody that uses a note outside the mode)

For instance, when I wrote a piece in G Lydian dominant scale (G A B C# D E F#), I used a key signature with only these two sharps (C# and F#). Then people have to find out about the key, and will then perceive all notes in that context.

The only exception to this for me would be if I am sure that the people reading and playing the music have no idea about these matters, and are inexperienced musicians. Then maybe I'd write in a G major scale (hoping they understand G as the tonic, and if not, at least seeing a familiar key) and lots of accidentals, making sure they notice these strange notes! :)


Actually, what I prefer is a bit unconventional. Please note that I'm not advocating this, because you might run into hot discussions.

For me, as a violinist, banjoist, guitarist and bassist, I'm expected to know that two flats means Bb or Gm. Almost all sight reading musicians knows what major key a certain key signature corresponds to. Fewer, but still many knows that Bb and Gm are the same. (They are not, but that's a different discussion)

Why not flip this around? Since musicians already know that two flats mean Bb, we can write Bb instead, and expect the musicians to know what that scale is. Instead of writing the key signature the conventional way and putting two flats there, just write in text that it's in Bb major. Or G minor. Or D phrygian.

Provided that the reader knows the modes (not trivial, but not harder than the circle of fifths, which most musicians do know) writing "D phrygian" gives all the information that two flats gives, plus more. It also gives the tonal center, and it can prepare the musician mentally for the phrygian sound.

In practice, if you're writing for someone else, it's probably not a good idea. The theoretical benefits are obvious, but music notation is built on tradition.

  • This is going to be messy when you get to accidentals and short modulations.
    – Gauthier
    Nov 17, 2021 at 16:32

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