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I am learning "A Hard Day's Night" by the Beatles which is in G Mixolydian mode or C major. In the score I have of this song the writer notated the song in G major and used accidentals on the notes that are not part of the G major scale. Why couldn't they have just used C major as the home key as all the notes pertain to that key?

Is this because the song keeps going back to that G chord? If this is the reason, it seems silly, because you could have a C major song with these chords in a bridge, and then it would be notated in C major.

Peter Mortensen
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    Closely related question here. I don't really believe, that G mixolydian and C major are similar, not to talk about exchangable, as suggested in the first sentence. – guidot Jul 16 '18 at 11:09
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    @guidot - they are more than similar in the notes each uses, they're identical ! But 'home' is a very different place. – Tim Jul 16 '18 at 11:21

3 Answers3

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I think the song is more ambiguous than you state. If the G chord contains an F, then the song is in G mixolydian, but if the G chord contains an F♯, then the song is in G major. The problem is that the chords aren't voiced with a 7th at all. If we turn to the melody for guidance, we find that the melody never contains a 7th over the G chord. We do hear the F in the melody, but only over the FMaj chord. However, we also hear F♯ in the melody (numerous times in the bridge).

So for the person notating, it's ambiguous whether the song is based on G major or G mixolydian. On the one hand, if they write the key signature with an F♯, they'll have to specifically mark the F♮s in the chorus. On the other hand, if they write the key signature with an F♮, then they'll have to specifically mark the F♯s in the bridge. So neither choice is perfect. Given that fact, choosing G major for the key signature avoids any additional confusion: no one will mistake the song as being in the key of C major.

jdjazz
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    This is why I generally assign key signatures based on the tonic and whether the music sounds more major or minor, not the mode it sounds the most similar to. I find that music, just like this example song, doesn't tend to strictly adhere to modes. – Dekkadeci Jul 16 '18 at 14:08
  • I don't think this is a good way of deciding between mixolydian and ionian. Blues uses minor sevenths almost exclusively, yet it's not really mixolydian. And many tunes don't use any chords with a ⅶ note in them at all (most typically, only switching between Ⅰ and Ⅳ), yet can be clearly classified as either ionian or dorian. Because these are mostly a melodic affair, and if the melody keeps going between Ⅰ and ♭Ⅶ then it's clearly mixolydian. – leftaroundabout Jul 16 '18 at 14:41
  • ...I'd say the verse is clearly in mixolydian, whereas the bridge is ionian. – leftaroundabout Jul 16 '18 at 14:44
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    Additionally, the bridge is...the bridge. It's fairly common to modulate to a different key in the bridge, which could explain the difference. – John Doe Jul 16 '18 at 15:37
  • @leftaroundabout I think this sounds sensible to me, the writer chose ionian in this case. I hadn't realised that it was ionian further on. That explains it! –  Jul 16 '18 at 17:52
  • Re my comment above: I don't know how that “dorian” slipped in there... — @armani, yeah, but normally when a piece changes key / mode that'll have no influence on what signature is used in the beginning. Either they'll change signature (when it's a significant modulation, like going to the parallel minor) or just stick to the signature of the beginning (in the development section of classical pieces, you often change so quickly through tonalities that it would be impractical to change signature every time, also you tend to move around the circle of fifths which means not that many accidentals. – leftaroundabout Jul 16 '18 at 19:39
  • @JohnDoe, I agree completely about the bridge. There might be indicators of a key change (lead in chords, etc.), or the new key might just sound different. I think neither is the case with this particular song; the bridge simply sounds like the relative minor of the chorus. I'll edit this into the answer. – jdjazz Jul 16 '18 at 22:27
  • @leftaroundabout, I see your point, but I don't think it's 100% clear cut. I7-♭Ⅶ7 progressions often emphasize the flatted seventh in the chord voicing, which doesn't happen in this song. Additionally, songs do exist with IMaj7-♭ⅦMaj7 progressions. This song is more ambiguous than either case because the 7th is omitted from the voicing and doesn't appear in the melody. On this song, playing a major 7th over the G chord (e.g., when soloing) could definitely sound good if resolved appropriately. By contrast, playing the major 7th over the C in Killer Joe would stand out like a sore thumb. – jdjazz Jul 16 '18 at 22:31
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I think that G Mixolydian uses the same notes as C major, therefore it should have the same key sig. - no # or b. It shouldn't really have a g major key sig., as it's not in G major.

However, it could be argued that because 'home' is a G note, when it's written in G (F# key sig.) and all the Fs are natural, it's a sign that it's not actually in G major, but G Mixolydian. But surely the main purpose of a key sig. is to obviate the need to keep using accidentals throughout the piece?

Your header hints of why Mixolydian is a major mode. Simply as it contains a major third above its root.

Tim
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    I disagree that the main purpose of a key signature is to avoid writing accidentals. Rather, the main purpose of a key signature is to signify the key. If you're notating something in minor, you don't worry about whether you're spending enough time in melodic minor that you could save some accidentals by writing it in major and lowering all the 3s; you always write it in minor, and the fact that there are lots of raised 6s and 7s is a strong signal that it is in a minor key and not the parallel major. I think it's not unreasonable to do the same for modes. – Micah Jul 16 '18 at 17:52
  • @Micah - we're probably agreeing here. The main purpose is to signify the key. Since modes have the key of their parent key, that's what happens. They never have a key of their own. – Tim Jul 16 '18 at 18:56
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    @Micah: Indeed, the "Dance of the Spooks" in the Thompson piano books is in D minor (one flat in the key signature), but there there are over a dozen B naturals and zero B-flats in the entire piece. – supercat Jul 16 '18 at 20:14
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Consider the song "Little Drummer Boy". If one writes the song with a key-note of G, the melody and some possible harmonizations would be devoid of F-sharps. On the other hand, the only F in the melody occurs in a rising passage where, in the absence of a printed accidental, a performer would likely be more likely to notice that the note is just below the key note of G (which, since the song seems to be in major, would imply that it should be just a half step below the key note, i.e. F#) than to remember that even though the piece seems to be in G, there's no F# in the key signature.

If putting a natural sign before the F would be necessary to ensure it gets performed correctly, having an F# in the key signature which gets canceled by the natural sign would be no less readable than omitting the F# in the key signature and using a cautionary accidental. Unless one is hand-transcribing a score, there's no need to try to minimize the total number of sharp signs on the page.

supercat
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