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victoria Williams Music Theory

Victoria Williams

LmusTCL BA Mus (Hons) MISM

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Next UK ABRSM Online Theory Exams Grades 1-5:
16th March 2021
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12. Key Signatures

Grade One Music Theory - Lesson 12: Key Signatures 

Suitable for:  ABRSM Grade 1   Trinity Grade 1   GCSE   AP Music Theory Beginners 



When we write music which mostly uses notes from the scale of C major and sounds good finished with a C, we say that the music is "in the key of C major" or "in C a major".  

Here's a short tune in C major:

Tune in C major - music theory

For ABRSM Grade One Music Theory, you only need to know about these three key signatures: G major, D major and F major, and for Trinity Grade One Music Theory you need to know G and F. (and you need to know that C major doesn't need a key signature!)


G Major Key Signature

If a tune mostly uses the notes from the G major scale and sounds good finished with a G, then the music is "in G major".

The scale of G major contains the notes G-A-B-C-D-E-F#. The key of G major contains F sharps, not F naturals.

Instead of writing all the Fs in the piece with sharp signs next to them, we write just one F sharp, right at the beginning of the line, after the clef and before the time signature.

This is called the "key signature".


In the treble clef, we always write the F sharp sign on the top line (we never use the lower F space). You should be able to just see the line of the stave between the two horizontal lines of the sharp sign.

In the bass clef, we write the sign for F sharp on the second line from the top.

G major key signature bass clef

The key signature is written at the beginning of every line of music, immediately after the clef, to remind us that all the Fs need to be F sharps.

(We don't use a key signature for music which is in C major, because we don't need one! - C major doesn't have any sharps or flats!)

The key signature is there to remind us that all the F's in the piece should be F#s. It applies to ALL the pitches of F, not just the one on the top/2nd line of the stave.


Here's the same tune as above, but now it's in G major:

Tune in G major - for grade one music theory students


F major Key Signature

Let's look at the key signature for F major next. Remember that in F major there aren't any sharps, but there is one flat - B flat.

F major key signature treble clef

In the treble clef, the flat is written on the middle line.

F major key signature bass clef

In the bass clef, the flat is written on the second line from the bottom.


D Major Key Signature (ABRSM Grade 1, Trinity Grade 3)

Finally, let's look at D major:

D major scale

(T=tone or whole step, S=semitone or half step).

The scale of D major has two sharps - F sharp and C sharp. This means that music written in the key of D major has F#s and C#s too.

The key signature of D major in the treble clef looks like this:

D major key signature for music theory students

We add the C sharp after the F sharp that we've got already. 

In the bass clef, the key signature of D major looks like this.
D major key signature bass clef