WHAT IS A KEY SIGNATURE?
To minimize the number of sharp / flat signs in the music, a composer starts the piece with a ‘key signature’ – which is a display of sharps or flats which remain in effect throughout the music:
You can identify which key a piece of music is in just by looking at this display of accidentals (plus a few other factors in the music).
There’s 12 major scales which exist, and each has a unique set of notes. In most cases this includes a number of black notes (called ‘accidentals’), which can be spelt using sharps OR flats – but never both. I don’t suggest memorizing the unique sharp / flat combinations for all keys (although you’ll start to remember most of them after a while). Instead I’d rather show you how to build any key from scratch – so that you never worry about forgetting.
IDENTIFYING A KEY SIGNATURE
Here’s how I identify key signatures quickly:
Sharp keys:
Look for the last sharp listed (furthest to the right). This will be the major scale’s 7th:
– So if F# is the last sharp – then the key is G major (just count up a half-step from the last sharp):
TEST YOURSELF
Before reading on, which major scales do the following 2 key signatures represent?
Key sig 1.
Key sig 2.
ANSWERS
In Key sig 1, the last sharp is C# – which means the key is D major.
In Key sig 1, the last sharp is A# – which means the key is B major.
Flat keys:
Look for the last flat listed. This will be the major scale’s 4th:
– So if Bb is the last flat – the key is F major (just count down a 4th to find the major scale’s root).
TEST YOURSELF
Before reading on, which major scales do the following 2 key signatures represent?
Key sig 3.
Key sig 4.
ANSWERS
In Key sig 3, the last flat is Ab – which means the key is Eb major.
In Key sig 4, the last flat is Cb – which means the key is Gb major (an extreme example, but still correct).
Relative Major / Minor Scales
But we’re not yet finished. Every key signature represents BOTH a major scale, and a minor scale – called ‘relative major and minor scales’.
So once you’ve identified the major scale, you still need to identify the relative minor scale – since the music could also be minor.
To find the relative minor scale, count down a minor 3rd from the major scale’s root:
Image – count down minor 3rd
So if the key signature represents G major – then it also represents E minor (a minor 3rd below G).
TEST YOURSELF
Before reading on, which major AND minor scales do the following 2 key signatures represent?
Key sig 5.
Image – Bb Eb
Key sig 6.
Image – F# C# G# D#
ANSWERS
In Key sig 5, the last flat is Eb – which means the key is Bb major – AND – G minor (down a minor 3rd from Bb).
In Key sig 6, the last sharp is D# – which means the key is E major – AND – C# minor (down a minor 3rd from E).
DISTINGUISHING BETWEEN MAJOR & MINOR
Most music these days (pop) sways back and forth between sounding major and relative minor, every few bars (covered in lesson 5 of The Musical Ear course). However some styles (classical) tend to stick to one or the other – major or minor.
In a music theory exam you might be asked to identify whether an excerpt of music is major or relative minor – just by looking at the manuscript.
So to establish whether the music is major or minor, first identify the key – the major AND minor scale that the music could be in.
Next look at the start / end chords – since most music starts and ends on the root chord of the scale:
Image – excerpt Bb major – starts ends on Bb major
Since the above excerpt starts & ends on Bb major – it’s probably in Bb major.
Whereas if the music looked like this:
Image – excerpt G minor – starts ends on G minor
Since the above excerpt starts & ends on G minor – it’s probably in G minor.
So that’s how I identify the key of any piece of music:
- Identify which major scale the key represents (look for the last sharp, or last flat).
- Locate the relative minor scale (count down a minor 3rd).
- Look at the start and end chordsto determine whether the music is major or minor.
MODES
One final point on key signatures (since I like to cover EVERYTHING):
Occasionally a key signature is used to represent a modal piece of music – like a piece written in the dorian mode for example (Click here to see my Modes Lesson).
The fact that the modes are built from the same notes as the major / minor scale means that a key signature could be used for a modal song too – to minimize the number of sharps / flats in the sheet music.
Although it’s quite rare for a song to be modal (maybe 2% of all songs are modal), occasionally I’ve seen modal jazz standards use a key signature.
For example, a song in C dorian mode (C D Eb F G A Bb) is perfectly entitled to use the key signature of Bb major (Bb + Eb):
Image – C dorian using Bb major’s key sig
Or a piece in C lydian scale (C D E F# G A B) might as well use the key signature of G major scale (F#):
Image – C lydian using G major’s key sig
The way I’d know that a piece is modal (just by looking at the sheet music), is if the start / end chords are NOT the major or relative minor scale’s root chords.
For example, if the key signature Bb + Eb – but the start and end chord is NOT Bb major or G minor. Then I’d widen my search to the modes:
If the piece starts / ends on a C minor chord – I’d conclude C dorian – because when I treat C as the root, and play up the scale with Bb and Eb – the dorian scale is what I end up playing.
If the piece starts / ends on a F major chord – I’d conclude F mixolydian – because when I treat F as the root, and play up the scale with Bb and Eb – F mixolydian scale is what I end up playing.
Of course to recognize which mode you’re playing, first you have to have learnt each mode’s interval pattern – see my modes lesson.
Again – modal music is quite rare, so focus on major / minor first. About 98% of music will be straightforward – major or minor.
Also see my next lesson – where I show you how to build a key from scratch with correct note spelling.