What to do if you don’t know the scale of the bottom note!

By Jade Bultitude
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Before reading on, please make sure you have visited the other interval blog posts and watched the relevant YouTube videos! In today’s blog we will be looking at what to do if you have a bottom note with a scale you don’t know?

Before starting let’s look at a few examples of intervals to refresh our memories!

What interval do we have below?

interval, interval of a 5th, fifth, diminished 5th

Remember to work out the distance between the notes first  (the number) first… 

D major, scale, degrees of the scale

A is the 5th note of the D major scale, making this interval a 5th.

Next step…

Is Ab in D major? 

No, it is not, we have an A natural in D major! 

piano, semitone, one semitone lower

As you can see on the piano we have come down by one semitone. This brings what would have been our perfect 5th into a diminished 5th

If you are unclear about why a 5th is perfect please read up in the other blog posts

What about this one?

interval of a 3rd, augmented 3rd, interval

What is the interval?

G major scale, G major, scale

That’s correct! It’s a 3rd! Is B sharp in G major?

No, it is not! We have a B natural in G major? 

To get to B sharp we have come up by one semitone, taking what would have been our major 3rd into an augmented 3rd!

Notice how these intervals are relatively simple to work out if you know what is in the scale of the bottom note! Make sure you are super confident with your circle of fifths up to 6 sharps and 6 flats and you will be very confident with this question! 

But what do I do if I don’t know the scale of the bottom note?

Sometimes you will be given a question where you simply do not know the scale of the bottom note!

Look at this interval below…

interval of a 5th, G sharp

Now, G sharp major is an extremely difficult scale… I bet you can’t tell me how many sharps are in it?!

So rather than struggling to figure out how many sharps are in G# major… bring this note down a semitone to G natural! 

However, you must remember, if you bring this note down a semitone to G natural then you must also bring the top note down as well to keep the interval the same! So, if we bring D down a semitone, we get to D flat!

This is our new interval…
interval of a 5th, G to D flat

An easier interval to work out! So, what is the distance between these two notes?

G major, G. major scale, scale

That’s correct, it is a 5th! Is Db in G major? No, it is not, we have a D natural. Therefore, we have come down a semitone. G-D would have been a perfect 5th but G-Db is a diminished 5th

Let’s try another one…

interval of a 3rd, A double sharp to C sharp

Now, do we know A double sharp major?! No, we don’t! 

So, let’s bring this down a semitone… 

piano, semitones

Well I don’t like A sharp major much either…. Shall we go down another semitone?

piano, semitones

A major! Much nicer! 

Now we have come down two semitones so we need to make sure we do the same to the top note… What is two semitones lower than C sharp?

piano, semitones

Two semitones lower than C sharp is C flat!

So now our interval looks like this…

interval, interval of a 3rd, A to C flat

Much easier to work out! Now what is the distance between these two notes? 

A major, A major scale, scale

The distance between A-C is a 3rd ! 

Is Cb in A major? Take a look at the A major scale above! 

No, it is not. In A major we have a C sharp – so how many semitones have we come down?

piano intervals, semitones

That’s correct we have come down two semitones! 

Music Theory, Intervals, diminished, augmented, minor major

Two semitones down from major brings us to diminished!

So, the answer to this question is DIMINISHED 3rd!

I hope that has made things a little clearer for you! Check out our worksheets to practice this further!

Have a great week!

Jade x

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AUTHOR
Jade is an experienced musician and teacher as well as being the founder of Music Theory Foundations. She has been helping people learn music theory for more than 10 years from pre school children all the way to degree level studies.