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I know that C major and A natural minor have the same key signature. Are they considered different keys though? Is modulating from one to the other considered a key change?

  • Modulation is the correct terminology for a key change – Neil Meyer Feb 8 at 14:07
  • @NeilMeyer - bet if you asked, far more would recognise and understand key change! – Tim Feb 8 at 17:03
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Yes it is a key change because functionally where the harmony is going is different. A key in general tells you two pieces of information: a general idea of harmony and the note you will sound at rest on known as the tonic. Even though they share the same notes, both the general harmony and and the tonic are much different.

To be in C major and to be in A minor look very different harmonically. In C major you'll typically use G or G7 to get back to C. When you factor in minor key harmony, which utilize the leading tone, in A minor you're most likely using E or E7 to get back to A. They are two distinct concepts.

  • so you're saying they're not the same key. weird, I thought a key was an unordered set of notes. I didn't know that diatonic functions played a role in it. – foreyez Feb 8 at 4:17
  • It does. It's why we make the distinction in the first place. If they were the same key we would not really need a distinction. – Dom Feb 8 at 4:19
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    @foreyez Strangely, a key tells the tonic, but a key signature does not. – user45266 Feb 8 at 5:23
  • @foreyez - diatonic notes are those which belong to a certain key. Those making up C major are not exactly the same as those making up A minor - unless A natural minor is used, with the G note rather than G♯. Whether the change from C major to A minor only using the nat. min. notes may or may not be modulation. Dom..? – Tim Feb 8 at 10:02
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Yes, C major and A minor are different keys. That's why they have different names!

The set of notes C, D, E, F, G, A, B has seven possible modes (though the one starting on B doesn't get used much). Two of them rate the special status of 'Key'.

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I would add to the previous answer that when one writes in a minor key the Harmonic and/or melodic minor scales are used to create resolution from the relative V7 to i (the vi of the relative major) by creating a leading tone in the minor key. With these accidentals in place you really cannot say you are in the relative major.

You don't need this device to hear the minor key. To "hear" minor you would need melodic lines and progressions structured in such a way that focuses attention on the minor scale. You could write a melody that focuses on the 6 and 9 of the I chord (example, A and D of C major) and that will not sound minor nor will it make sense to say you are playing in A minor. But adding G#, and possibly F# in the melody line to move into A, or having progression or vamp like A- --> D-, etc will definitely sound minor.

It's a combination of these factors that distinguishes "key".

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Yes, because the tonic changes.

You can get into the details of the changing chord functions, the leading tone etc. but I really think it is as simple as changed tonic = changed key.

  • right to the point, tnx! – foreyez Feb 8 at 15:48
  • but if you don't change the tonic does it still change the key. So from C to C dorian? – foreyez Feb 8 at 15:50
  • That was discussed in some other posts. The idea is call that a 'mode change' rather than 'key change.' And I understand the point being the tonic does not change, but the color of the harmony changes. In technical language just the mode changes. – Michael Curtis Feb 8 at 15:57
  • Also, some may take issue to calling Dorian a key as it doesn't have a leading tone. Dorian is modal not major/minor system. Key is a notion specific to major/minor system. – Michael Curtis Feb 8 at 15:58
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    Not the same key. But I think the question was about what to call that specific kind of change. Not 'closely related.' I think also not 'modulation' as the tonic doesn't change. I don't remember all the earlier posts. It might be worth posting as a new question. – Michael Curtis Feb 8 at 16:19

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