When it comes to music theory, key signatures are an essential part of making music easier to read. They also allow us to know which accidentals we should use and what key we’re playing in.
What is a key in music?
If a piece of music uses notes from one particular scale then we’d say it is in that ‘key’.
For example, if a piece of music uses only notes in G major scale then it would be in the key of G major.
Or, if a piece of music uses only notes in F major scale then it would be in the key of F major etc.
The example below is in the key of G major as it uses only the notes from that scale.
What is a key signature?
When writing out music in a certain key we’d have to write in a sharp or flat every time that note came up.
If you were to do this in some keys then it can mean adding in a lot of accidentals and the music can get very cluttered.
However, to save us from having to add all the sharps or flats each and every time when we’re playing in a given key, we use a key signature at the beginning of the music to make it easier to read.
For example here is that same melody but using a key signature.
Instead of writing a sharp in front of every single F, we just write one at the beginning which then tells the musician to play an F# every time.
Even the F that is in the first space of the stave.
If the piece was in D major it would have an F sharp (F#) and a C sharp (C#) as its key signature because D major has two sharps.
For example, this piece in D major without a key signature:
But with a key signature it becomes this:
Another example of a piece in F major without a key signature:
But with a key signature it looks like this:
A piece in C major obviously doesn’t have any sharps or flats in its key signature as there aren’t any black notes in C major scale.
Where does the key signature go?
The key signature is always written after the clef but before the time signature.
It’s important not to write it after the time signature as this is a common mistake beginners make. s
The order of key signatures
When writing key signatures you can’t choose any old order of the accidentals. There are a few rules that you have to follow.
The first rule is that you can only use either sharps or flats. Never both.
It’s important to always put the key signature in the right place.
For example in the treble clef, F sharp (F#) is always on the 5th line of the stave but in the bass clef it’s on the 4th line.
Here are the three key signatures in both clefs.
Hopefully, that helps you make a bit more sense of key signatures. I’ll be adding to this post soon going over the other key signatures plus the different clefs like the alto and tenor clef.
In the mean time, I recommend making some flashcards to help you memorise them.