How do you derive a minor key from a major key? [duplicate]

Question

So I learnt that going to the sixth note of a major key will give you its relative minor - with the same key signature.
How are you supposed to know what notes will be in the minor key?
Are they the same notes as the major key since the key signatures are the same?

Answer 1

There has always been a problem with this concept. Hopefully, this will unravel it all.

It's true that the relative minor of a major key is found by counting up 6 notes from that tonic. So key C major - CDEFGA - A minor.

It's partly true, in that those same seven notes constitute the relative minor scale.

THE PROBLEM is that 'minor' contains different sets of notes, all of which get legitimately used in minor compositions. Check out melodic and harmonic minor scale notes.

The natural minor set of notes is exactly the same for a major key and its relative minor. As in key Cmaj. CDEFGAB, scale A natural minor ABCDEFG.

So far, so good. But then we have other notes which manifest themselves, for various good reasons, in minor keys. They are specifically the raised 6th and raised 7th notes, compared with natural minor. So, key A minor can, and does, use F♯ and G♯ as well. Problem for a lot of learners is those two notes are NOT reflected in the key signature.

It would seem to make sense, since at least G♯ occurs a lot in pieces in A minor, that the key sig. should reflect this, and show G♯! Not doing so is witholding vital information! But we don't, so there! In fact, some composers did start showing suchlike, but it never caught on. Pity in a way - it might have been a reason not to ask this question!

EDIT: I notice that you tag scales and keys. Please note that they are not the same as each other, although a lot of folk seem to think they are. In fact, the first sentence in the question implies this. Not key, but scale.

Answer 2

Parallel Minor

Starting with a major key – say C major:

C D E F G A B C

To get the parallel minor of C major, we change the major seventh, major third, and major sixth – to become a minor seventh, minor third, and a minor sixth respectively. These changes will be also be reflected in the key signature – now three flats. But the key is still C. This is C natural minor:

C D Eb F G Ab Bb C

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If we want the C harmonic minor scale we raise the seventh back up (to be a leading tone):
[using n for the natural symbol]

C D Eb F G Ab Bn C

The C melodic minor scale has different notes depending on which direction we are playing it. Its ascending form has a major sixth and major seventh, while its descending form (like the natural minor) has a minor sixth and minor seventh :

C D Eb F G An Bn C Bb Ab G F Eb D C

Relative Minor

But, your question was about the relative minor. As you said, if we take a major key – say C major and play a scale starting on the sixth note we do get a minor key: C major's relative minor is A minor.
The key has changed (from C to A), but the key signature will not change (still no sharps or flats).

The A natural minor scale is:

A B C D E F G A

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Again if we want the A harmonic minor scale, we will have to raise the seventh:

A B C D E F G# A

Or if we want the A melodic minor scale we will have to raise the seventh and the sixth on the way up, but not on the way down:

A B C D E F# G# A Gn Fn E D C B A

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So to answer you question more directly:

The notes in a major key's relative minor, depend on which of the scales (natural, harmonic, or melodic) of the minor key you are using. If you are using the natural minor, the notes with be the same notes as the notes in the relative major. But if you are using a different scale some notes will have to be modified.

Answer 3

Your issue comes from confusing the concepts of scale, key and key signature. A key signature defines a set of pitches, but a key only defines a home note and its third. Within a key, all possibilities are open to use notes and scales, as long as the sense of home is preserved.

Below is a song that is very clearly and deeply in the key of A minor. The key signature does not specify any sharps or flats, but still, all black keys of the piano are needed. The tonic chord, i.e. the home chord is the A minor chord. Which is really the only thing that is meant by saying that the song is "in A minor".

Key is more about the tonic than any scale. A key is not harmonic or melodic or pentatonic or Dorian or Mixolydian or Blues. The key tells you two things: (1) a note name giving the home note i.e. tonic, and (2) the type of the home chord i.e. tonic chord, is it major or minor. The major/minor thing does not mean a list of "allowed" notes, it means the harmony around the home note.

Since the tonic chord already specifies the tonic note, we can simplify the formula of key as:

• KEY = TONIC CHORD

... and accordingly, the name of the key follows the name of a basic chord. "This song is in A minor." A minor, the chord, not A minor, the scale.

When you're told that a song is in a key, it is to let you know what the prominent home note is, and whether the home chord is a major or minor chord. A wide variety of different scales and harmonies may be used, and the harmony may be almost anything during the song, changing and mixing harmonic feelings from different scales back and forth, but as long as the home chord stays the same, it will be in the same key.

However, you can assume a default reference scale based on the key. The reference scale is the notes you get from the key's key signature. For example if a song is said to be "in A minor", then you can assume the A minor natural scale as a basic reference grid to which you relate the song's actual harmony. For example if there's an A major chord somewhere in the song, you'll note that as a somewhat remarkable point, because an accidental is needed for writing the C# note.

A very similar thing was asked not many hours ago, but it was closed as being unclear (allegedly). I reused much of the same text, since the question was declared as a non-question (because it wasn't possible to figure out what was being asked, i.e. which problem the answer solved)

Answer 4

This answer is similar but perhaps has a bit of a different point of view. A scale is just a bunch of notes listed in (ascending) order. A key is a set of relations among these notes. One note is treated as the tonic and then a bunch of chords are assigned relations based on which note is the tonic.

A major key is easy. These notes when written as a scale (based on C so it looks nice on a keyboard) are C-D-E-F-A-B-C but the important thing is the arrangement of whole steps and half steps with the tonic at each end: W-W-H-W-W-W-H. This all came about historically but that's another story.

Each major key has two closely related minor keys (and vice versa). One is the "relative minor" which shares the same key signature; the other is the "parallel" minor which shares the same keynote. (Other languages may use different terminology.) Both minors share the same structure but different tonics.

As they share a key signature, the relative minor scale is a cyclic permutation of the notes of the relative major starting a minor third below the major's tonic or a major sixth above (octaves are considered equivalent). That's a fancy of saying the notes, C-D-E-F-G-A-B-C can be written A-B-C-D-E-F-G-A with the A treated as the tonic. The relations between the relative scales can be seen here. The triad based on the major tonic is C-E-G, which is a major chord; the triad based on A is a minor chord.

To go from the major key to its parallel, one lowers some notes (using flats or naturals whichever is appropriate) and creates the minor scale arrangement. C-D-Eb-F-G-Ab-Bb-C.

Almost there. Just rearranging the order (to make the usual final chords be on the lowest scale step) isn't the whole picture. The real difference between major and minor is that in the minor, scale steps 6 and 7 are mutable. These steps are used in two forms, the "nominal" or "lowered" from and the "sharpened" or "raised" form. So in C minor, scale steps Ab and Bb may be raised. (There are common procedures but mostly it depends on one's "ear.") For historical reasons, occurrences of these scale steps are given different names, but composers use all combinations in the same piece quite often, sometimes in the same phrase or even different versions of these scale steps at the same time.)

Summary. From C major: C-D-E-F-G-A-B-C is related to A minor by permutation A-B-C-D-E-F-G-A with F# and G# occurring commonly. C major is related to C minor by C-D-Eb-F-G-Ab-Bb-C with Ab and Bb occurring as A and B rather commonly.

In some other place on this site, I have posted several notes about where the minor key mutates steps are used. (Its about as long as this answer.)

Answer 5

"So I learnt that going to the sixth note of a major key will give you its relative minor - with the same key signature."

This is correct. For example, the relative minor Key to Bb Major is G.

"How are you supposed to know what notes will be in the minor key?"

This question could be interpreted in more than one way. A knee-jerk response might be all the same notes that were in the major key you started with, but that assumes you always start with a major key and this isn't necessary. It should also be noted that playing in the "minor" scale or more is NOT the same as writing music in a minor key.

The minor scale does not have a leading tone so it is inserted by sharpening the 7th degree that naturally occurs in the minor scale to create harmonic minor. This introduces an augmented 2nd (enharmonic to a minor 3rd in equal temperment) from the 6th degree to the now sharpened 7th degree. The 6th is then also sharpened on ascending passages to create the Melodic Minor scale, which has the sharp 6th and 7th removed in descending passages. This is the scale most often used to write melodies that are "a minor key". However, the key signature is not altered. As an example, a song written in the key of A minor will have no flats or sharps in the key signature but you may find many occurrences of G# and F# in the melody and chords.

I would like to point out that while the connection between the modes of western music is interesting it isn't necessary for determining the notes of a mode. Each scale has its own sequence of steps. If you know the sequence you can figure out what notes should be in the scale. For natural minor the sequence is W-H-W-W-H-W-W (W = whole, H = half). Start on any note and just walk up the alphabet. If the next note does not respect the sequence then either sharpen or flatten it. You will never have a mix of sharps and flats. As an example, the D minor scale would be built as follows: start with the sequence {D, E, F, G, A, B, C, D}. Now ask what are the intervals, W-H-W-W-W-H-W. Clearly this is not correct (it is D Dorian, in the key of C). To make it right we need to flatten the B, {D, E, F, G, A, Bb, C, D}. This fits the step sequence. Now to be in the "key" of D minor you would want to sharpen the Bb and C when you ascend, and leave them natural when you descend, {D, E, F, G, A, B, C#, D} --> {D, E, F, G, A, Bb, C, D} would be D melodic minor.

You will notice that the key signature is the same as F major, and D minor is the "relative minor" to the key of F. But you don't need to start there.

"Are they the same notes as the major key since the key signatures are the same?"

Based on the discussion to the previous question not necessarily. One can use the minor mode when composing a song in a minor key but it will lake a V7 chord which is needed to create a resolution to the root chord of the minor key. This is why harmonic and melodic scales are used in minor keys.