Excellent question – 21 Guns by Green Day – is it in D minor or F major? And how to tell?

After all, both scales share the same notes:

• F G A Bb C D E F. F major.
• D E F G A Bb C D. D minor. Same notes, just started on a different root.

Why is that?

D is the relative minor of F major. D is the Aeolian mode. D is the sixth mode. Whatever you wanna call it, the two go together and F will be on the outside rim of the cycle of fifths sporting one flat, and D minor will be right below it (typically inside the circle).

I think one of the most important skills as an informed band mate you can possess is to know the correct key of a song.

Especially when you work with singers, that comes in really handy!

This article gives you a great summary on how to find the key of a song. Hint: it is usually not the first chord, but rather the last! It lists simple guidelines and rules and all exceptions I could think of. I like complex stuff put in simple and memorizable terms, so check it out if you haven’t read it before. I think this stuff is must-know for a bass player! After all, we deal with roots all the time!

Now this 21 Guns song a Quoran is asking about exemplifies an ambiguous key center. I make a case for what I think it is – what do you think?

If you check it out, you also get rewarded with a hilarious video by an Australian comedy band, talking about four note chords. Incidentally, 21 Guns is exactly one of those. Just in a different order, hehe.

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Read Ariane Cap’s answer to How do you know when a scale is in a major or it’s relative minor, when the notes are same? Is 21 Guns in F major or D minor? on Quora