Most classical musics begin in a key that matches its inital key signature, but some songs doesn't.

For example, Schubert's impromptu no. 4, op. 90 begins in A-flat minor, but its key is A-flat major, according to wikipedia or other classical music dictionaries. It begins in A-flat minor, modulates to C-flat major, then B minor (probably respelled from C-flat minor), then finally A-flat major.

How to find the key of songs like that?

P.S ) His D.774 also begins minor key, despite of major key signature. Is its key A-flat minor?

  • 2
    This is going to be sullied by my experience reading the sheet music of self-published works that clearly use the wrong key signature (I've even seen such disgusting things as F minor music written with an E minor key signature and too many sharps instead of flats).
    – Dekkadeci
    Feb 24, 2023 at 6:35
  • 2
    Why does a piece of music have to have a single key? OK, in the classical period it was the rule, but since then anything goes, and the example of Schubert is a good one. By the way, it's not a "song" - there's no singer there!
    – Peter
    Feb 24, 2023 at 18:14

3 Answers 3


The key of most pieces is that posted by the composer. After all, that's what they decided upon. It might well be, as in this case, the piece modulated into the parallel and relative keys, or indeed any other key that the music strayed into. But it's all really academic, and won't make much difference. Or will it? What's to be gained by considering that several bars or even a section is in fact in a different key from that quoted?


The tonica is „the place“, the „save harbor“, where the music resolves to, after all kinds of journeys (modulations) and tensions (e.g. dominant, subdominant).

So the end of the piece (or phrase), not the beginning, is where to look at. As you described, it resolved to A major.

The rest can be explained by, e.g.:

  • curiosity
  • „fooling“ the audience a bit
  • esthetics
  • a certain logic followed (or none)
  • a story told musically
  • and so on

In terms of degrees, using small letters for minor and capital for major, the overall journey you described is:

  • i - III - ii - I

which creates its own atmosphere as a musical idea.

  • Thanks for your answer. Then in case of D.774, should its key be understood as A-flat minor?
    – cplex
    Feb 24, 2023 at 7:08
  • I don‘t know D.774, but you wrote, it ends with A major chords. So key A major.
    – MS-SPO
    Feb 24, 2023 at 7:16
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    @MS-SPO - Funnily enough, I've seen way more examples of pieces being labelled as the key they begin but not end in (e.g. marches like Sousa's "The Stars and Stripes Forever", sonata-allegros that start in a minor key and end in the tonic major, every pop song ever with a Truck Driver's Gear Change).
    – Dekkadeci
    Feb 24, 2023 at 10:58

It’s a pretty basic principle of the Classical style that keys are used structurally. A piece starts in one key, travels through some contrasting keys, but completes with a satisfying return to the original one. And that idea persists in a lot of today’s popular music. But some songs (and some symphonies) start in one key, end in another. It’s pointless to try to ‘determine’ the overall key when there isn’t one.

But starting in A♭ minor, ending in A♭ major, the parallel major, hardly counts as not ending where it started. Neither would ending in the relative major. Think of it more as an extended Tierce de Picardy, the single major chord that often ends a minor-key piece. Go with Schubert (and with Tchaikovsky in his 5th symphony ‘in E minor’ but which ends in E major). Title it for the key where the bulk of the piece resides.

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