I was just a little curious, I've seen very little sheet music that uses modes: when transcribing or reading music in a perticular mode, does the key signature reflect the mode or does it reflect the tonic?
For example, if I wanted to write something in F lydian, would I use the key signature of F major and just add the natural every time I use the 4th of the scale? or would I use the key signature of C major? (since lydian is a parallel mode of C major)
Again, this isn't very urgent, I was just curious 8)
Steve-0
The key signature reflects the tonality; the melody shows you the modality.
If you were in C Dorian, you'd use the key signature for Bb, rather than flatting every B and E in the piece. It makes it easier to read.
Keeping things easy to read is the standard rule of thumb. If there's a disagreement between the melody and the harmony, it's usually the harmony that's kept simple to read - because chords are harder to read at sight than single notes. So if you're doing a piece with chords in the key of A, but the solo uses the A pentatonic minor, you'd use the key signature of A major, and use naturals for the melody notes of C and G.
Guitar teacher offering lessons in Plainfield IL
Both ways are certainly possible, but from what sheet music I have available, it seems more common to choose a key signature that takes the mode into account (e.g., F Lydian = no sharps or flats) if the music is fairly complex (or very old, e.g., Medieval or Renaissance periods). But for simpler music such as folk songs, it seems more common to choose a key signature that's readily associated with a major or minor key.
For example, the Dorian mode song Scarborough Fair is often written using a single B flat in the key signature depite having B naturals rather than B flats in the song. As it's an obviously 'minor' key song, it's assumed to be in the key of D minor (purely because D minor employs that key signature). This makes for less confusion among learners at a certain level who are learning about keys but have no idea what a mode is. They know only that a song is in either a major or minor key and expect to see a key signature associated with that key.
And that's how it should be IMO. If I've been teaching a beginner student some basic keys and associated key signatures, I don't want them asking why I've chosen a key signature that doesn't seem to match the key of the song, because at that level, an understanding of modes is the last thing they need.
Even publishers/ transcribers may be blissfully unaware if a song is in a particular mode other than major or minor. So even though a song may be in D Dorian, to all intents and purposes it's in the key of D minor and the appearance of B naturals within the song may be just seen as chromatic alterations - in the same way that certain notes of the melodic and harmonic minor scales appear as chromatic alterations within the music.
