It's always seemed strange to me that key signatures don't indicate the tonic. I feel this has two main drawbacks:

  1. Beginners (and more advanced students, it has to be said!) often find it difficult to determine the key signature from the sharps/flats alone.
  2. There is ambiguity between the major and the relative minor (and other modes).

I know the sequence of sharps and flats is fairly easy to learn, and that it helps you learn the circle of fifths, but it seems to be an unnecessary mental step. I can't help thinking that it would make it easier for beginners to learn to read music and to learn the basics of music theory if the tonic was clearly indicated in the score.

I find that players who don't read music often have a greater awareness of what key they're playing in than those who do, and I think this is one of the reasons. If you've got the sharps/flats written out then you can get away without thinking about what key you're in, which is a bad habit to get into.

Is this just a historical accident? Are there alternative notation systems which do clearly indicate the tonic?

  • You are right: Many compositions are even by the title explaining in what key they are written. Also In Pop music naming the chords indicate the key.... Commented Feb 26, 2019 at 13:07
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    A lot of the more serious music - classical, orchestra, etc. - will modulate a fair bit, so having a key and thus key sig. isn't too intuitive. Most popular music songs will stay in one key through their 3 or 4 minutes, and the key sig. there tells all. Looking at two sharps tells most musos it's either in D or Bm - not that many modal pieces around generally - so it's no great burden. If the vocalist points four fingers in the air,I know the next key is E. And you haven't got the #/ b written ; they're at the beginning of each line to save that. Even sight-readers should be aware of the key.
    – Tim
    Commented Feb 26, 2019 at 13:33
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    Books and movies sometimes fail to clearly declare who the bad guy is, and even worse, if it's going to be a happy or sad story. Such ambiguity is not good. Am I supposed to figure it out all by myself, as if it was a matter of opinion and interpretation or something??? ;) Commented Feb 26, 2019 at 15:51
  • @piiperi there's perhaps a distinction between the concept of some 'fact' isn't known at the start but becomes apparent, and something that remains highly nebulous even once the work has played out. The former might in some cases be useful knowledge to tell the performers up front (although sometimes actors aren't told the plot as a creative choice!) Commented Feb 26, 2019 at 16:35

5 Answers 5


"Historical accident" is one way to describe it. Historical oversight might be another.

The fact is we have never symbolically indicated the tonic in written music. D Dorian looks just like G Mixolydian - and after we discovered that there were notes between the letter named pitches and created key signatures, G Dorian looked just like C Mixolydian.

A key signature indicates a tonality (in the sense that it tells you the set of tones to be used) and not a modality (which of those tones is home base). Even though we call it a "key signature" it's more of a "pitch-class-set" label. But we didn't have the concept of pitch-class-set when it was given the name "key signature", and it takes quite a bit of effort to overcome six or seven centuries of tradition.


Is this just a historical accident?


Everything about music notation is a historic artifact!

When you go back a very long time - into the Middle Ages - there weren't key signatures and the tonic was called the final which was literally the last note. Interestingly the system of notation also did not indicate absolute pitch, the singers sang at whatever pitch was comfortable.

Way back then the tonality (the modes) could have been one of many modes. A flat sign was used, but not exactly the same way it's used for a modern key signature. The final would indicate the mode.

Eventually today's key signature system evolved and instead of several possible modes with different finals fitting into the key signatures we just have two choices major and minor. If we see a key signature of one flat we basically know it's either F major or D minor. If the music was modal, we would have many possibilities: G Dorian, A Phrygian, Bb Lydian, C Mixolydian, etc.

The key signature never really tells us what the tonic is. It's more of a device to transpose the diatonic gamut - the musical letters A B C D E F G. That may sound strange. Most people aren't taught key signatures that way. Basically you just memorize the circle of fifths and the corresponding major/minor tonics.

Looking at the end of the music is still the quickest way to determine the tonic of most music in the major/minor system.

This may interest you, but it's probably too much reading...

...sorry I can't verify the original source. It seems to be a chapter out of textbook.


The short answer: because it's redundant.

The slightly longer answer: because one of the things beginners have to learn is what sharps and flats belong to what key, not to mention the relationships between major and minor keys.

The full-length answer starts with: all but the most simple pieces go thru many modulations and keychanges or modes, so at best all you would know is the underlying tonic. There is a [redacted] of a lot more to learning music than just knowing the tonic, and ultimately it's one of the less important items when analyzing the full structure and progression of a composition.

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    I don't quite understand how the short and slightly longer answer relate to the question. You might have learned perfectly well what sharps and flats belong to what key, and the relationships between major and minor keys (and the other modes), but still not be able to tell by sight which of those keys or modes a piece is in. And if standard notation is based on the assumption that most pieces go through many modulations, why have a notation system that assumes one particular key signature in the first place? Commented Feb 26, 2019 at 12:54
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    Yes, but if it's redundant why not just indicate the tonic, and leave the performer to work out the sharps and flats? It would save ink. Commented Feb 26, 2019 at 15:34
  • @Bob don't be silly. :-) . Not to mention that the key signature need not be a standard scale. Check out Bartok. Commented Feb 26, 2019 at 15:37
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    @topomorto As Miles Davis said, "Play it and I'll tell you what it is later." There's no need to know the tonic, or even the major/minor/mode , to be able to play the sheet music as written. Commented Feb 26, 2019 at 15:39
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    @CarlWitthoft I think Bartok must have been off school when they taught key signatures ;) Commented Feb 26, 2019 at 15:45

It is a lot like a language, that evolves as result of common use and compound effect of minor corrections and then we end up with something that works really well even though it is not perfect and could in places be engineered into something neater and simpler and uniform.

Main purpose of score is strictly practical - a performance and learning aid and I think to show which notes are consequently sharpened or flatten in a piece is all information performer needs (that's where the fingers should be ready to go).

Also the fact that Key Signature is called that way might give impression that it's there to define the key of the tune. Well all it gives is a practical proxy to establish the key, and key of the tune actually can be sometimes up for a debate - it is not a definite information as opposed to definite information about sharps and flats. It's a bit of an abstraction on top of sharps and flats.

Finally one can call it ambiguity, and another - a very informative practical unification that tells us that from the performance point of view A minor C major and D dorian are essentially the same sets of notes


Pieces tend to modulate--or tonicize--often. Not all key changes are associated with key signature changes. The key of a piece, or more often a section, may be ambiguous. Combine these three reasons and an additional marking for the tonic in a key signature becomes clutter, useless, or even actively harmful.

Baroque music modulates fairly often. Fugues often put their first answer in the dominant key of the home key, yet they often do not change key signatures at all. Other contrapuntal music such as minuets and preludes also tend to change keys without changing key signatures. Note that Baroque music often contains the overall key of the piece in its name, yet those do change keys.

Classical music also modulates fairly often. The convention for sonata-allegros of the time is often to either refuse to change the key signature at the development or to strip the key signature at the development for chromatic enough development sections (e.g. the printings of the 1st movement of Beethoven's Appassionata Sonata I'm familiar with). Yes, this is the convention of the part of the sonata-allegro that modulates the most. Another convention is to not change the key signature of the sonata-allegro during the entire exposition, despite invariably changing keys halfway.

The key of pop music is sometimes ambiguous--is that song in a major key or its relative minor? I personally have encountered that problem when trying to determine the keys of Kelly Clarkson's "Behind These Hazel Eyes" and Avril Lavigne's "When You're Gone": both pieces have (at least seemingly) major-key choruses, yet they end the choruses with chords that match the tonic of the relative minor.

I'll pause here to note that, almost by definition, tonicizations are pretty much never associated with key signature changes. This is because of their temporary nature.

And, sometimes, it's ambiguous whether a phrase involves a tonicization or an outright modulation. Is the very early shift to E flat major music in Jon Schmidt's "Road Trip" a full modulation, or is it a tonicization because the music weaves out of and back into C major in a mere 4 bars? At any rate, the sheet music of Road Trip does not change key signatures there (at Bar 5).

Given these examples, it should be apparent why an additional indicator for the tonic at a key signature is often counterproductive.

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