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We have seen how some keys have the same key signature as each other, and here we look at this in a little more detail.
Sharing a tonic
There is a strong relationship between major and minor keys and their corresponding scales.
Every major key has a corresponding minor key starting on the same tonic: C major, and C minor, for example, both have C as the tonic. These two keys have a different key signature, however: C major has no flats or sharps, and C minor has three flats.
These pairs of keys are called parallel, so we can say that "C major is the parallel major of C minor", and that "C minor is the parallel minor of C major".
We can also say that C major and C minor are parallel keys.
Here is another pair of parallel keys with quite different key signatures, G major and G minor:
Sharing a key signature
You will have encountered many keys, so far, that share the same key signature but have a different tonic. An example of such a pair would be F major and D minor, which both have a key signature of one flat.
These pairs of keys are called relative keys, and we can say that "D minor is the relative minor of F major", and that "F major is the relative major of D minor".
Relative keys should not be confused wth parallel keys!
Here is another pair of relative keys, A major and F sharp minor:
Remembering the parallel key
Although parallel keys appear at first glance to often have completely different key signatures, there is a pattern to them, which might help you remember key signatures overall.
Look at the two key signatures of F major and F minor, and also C major and C minor (which are, of course, both pairs of parallel keys!)
You can see immediately that C minor has three more flats than C major, and that F minor has three more flats than F major.
In fact, this pattern applies for all parallel keys: so you can tell immediately that an unfamiliar key such as A flat minor has seven flats, because A flat major (a much more familiar key) has four flats, and 4+3=7.
What about sharps?
But what about sharps?
"Adding a flat" is equivalent to "removing a sharp". So, for example, to "add three flats" to G major, we get to a key signature of two flats:
- Start with one sharp
- Remove a sharp / "add a flat": no sharps or flats
- Add two more flats for a total of three added: two flats, the key signature of the parallel minor, G minor.
This system also works in reverse. To get from a minor key to the parallel major, you simply remove three flats, or if you prefer, add three sharps (both operations are identical!)
Here in graphical form is the process of getting from D minor to the parallel major, D major:
The main thing to watch out for in this simple system is C major, which of course has no flats or sharps.
Don't just leap straight from one flat to one sharp - you have to remember to go through "zero" (no flats or sharps) on the way!
Remembering the relative key
Although at first it might seem that the relative keys are randomly distributed, this is not the case and there is an equally simple pattern linking relative keys as there is for parallel keys.
As stated above, the relative minor of A major is F sharp minor, and also the relative minor of F major is D minor. Let's look at these two pairs of tonic notes and the intervals between them:
As you can see, both of the intervals are a minor 3rd. It turns out that the interval between the tonics of all pairs of relative keys is a minor 3rd.
We can immediately say, therefore, that the relative minor of an obscure key such as C flat major is A flat minor; and if we can remember the key signature of one, then we can instantly know the key signature of the other.
When using this technique, remember to use a minor third and not a major third!
If you use a major 3rd, you will get the wrong answer!
Up and down
You just need to remember that you go down from the major tonic to get the relative minor, and up from the minor tonic to get the relative major.
If it helps, you can think of "minor" as "sad and down" and "major" as "happy and up"!
Similarly, when remember the rule for the parallel minor, rememeber that you "add three flats" - a "lowering" operation, again thinking perhaps of "low, down, sad = minor"!
Learning key signatures
Both of these systems of parallel and relative keys can be a huge help to you when you are learning all the key signatures.
You just need to remember two "rules of three":
- To find the minor key signature if you know the major that starts on the same note, add three flats.
- To find the minor key name if you know the key of the major, go down a minor 3rd from the major key's tonic.
You can therefore safely memorise just the major key signatures, and these two rules, and you will instantly be able to know the minor key signature from the name, or the name of the minor key, if you have the key signature.
These two systems are both related in a subtle way.
Remember that a minor 3rd interval consists of three semitones stacked together. Remember also that a flat accidental lowers a note by one semitone.
Therefore "add three flats" is just another way of saying "lower by three semitones"!