Why is the key signature not the same as the listed key?

Question

Looking at the following piece, the information says that the key is G minor. However. the score in the "original key" has a key signature of D minor. Moreover, the score transposed to A minor has a key signature of E minor.

I am aware that:

1. The music is not strictly in a minor key, but rather in a mode, although I don't see why this would have any effect.
2. There are accidentals next to the notes that make the music effectively be in the listed key (so for G minor, the E's are notated with a flat to make it sound G minor, although with a signature of D minor).

I'm not sure if this is bad editing and if when I arrange the piece I can/should use the listed key as the key signature. Or maybe it's some convention that I've yet to see in this type of music.

Answer 1

You see this occasionally in Bach as well! Check out this piece in D minor:

The short answer is that, as musical practice was settling towards tonality, some composers were still using key signatures that, by today's standards, are missing a flat. These key signatures typically arose because the composer was using a transposition of a church mode.

In effect it looks like the pieces are being written in Dorian if you go by the key signature and ignore the later accidentals. (In fact, the Bach piece above is sometimes given the nickname "Dorian"!) But since the accidentals are there, it's just a piece in minor.

Answer 2

The key signature takes the form it does because the Dorian and minor modes were considered very nearly synonymous by many, possibly most, Baroque theorists (including Rameau). Dorian mode was seriously considered to be the precursor to the minor mode. There were a couple of reasons for this:

• the standard mutable tones for the Dorian mode were 6 and ♭7 (e.g., B and C in D Dorian), the former frequently being flatted (particularly, in imitative counterpoint, in tonal responses that turn toward the subdominant region, as happens in the Schütz example), and the latter being raised (particularly in cadences).
• The Dorian mode, like the major mode, requires only that the 4th degree be raised to accomplish a perfect cadence to the dominant. Contrast that with the Aeolian mode, where both 4 and 6 must be raised to cadence to the dominant.

Answer 3

Baroque (and some Renaissance) key signatures are often written with one fewer flat than is commonly used now. (Sharp keys seem to sometimes use one less sharp but I think I have seen one more sharp too.) There are some studies on the matter but most are not freely available on the net. Wikipedia has a short paragraph about this practice under "Key Signatures."

It's been suggested that one may need fewer written accidentals with the Baroque version. (There are also suggestions in various publications and on various net sites that minor keys should have "harmonic minor" signatures.)

I did a bit of counting by hand (mostly Bach, and a few other short pieces) to check if the number of written accidentals (those not in the key signature) would be smaller. I didn't find much difference (but I didn't keep the results as the sample was small and perhaps not representative.) The current practice of using the key signature of the relative major has the advantage of being regular and not needing extra variations for various modes.