Theory of Music: Key Signatures

This page explains my method for working out the number of sharps or flats in a given key signature (or, vice versa: working out a key, given the number of sharps or flats in its signature). Like a lot of my methods, you may find it somewhat arcane; but (I hope) the more you use it, the clearer it will become.

I am indebted to Wikipedia – which credits Schonbrun, Marc (2005): The Everything Music Theory Book, p.68. ISBN 1-59337-652-9 – for the following mnemonic:

Father Charles Goes Down And Ends Battle

As we noted on the Music Theory page, this tells us the order in which the sharps appear; in other words, if a key has one sharp, that sharp is F♯; if it has two sharps, they're F♯ and C♯, and so on. But that's not the only way that this mnemonic can help us.

Consider the following three tables:

	F♭	C♭	G♭	D♭	A♭	E♭	B♭
Major		7 flats	6 flats	5 flats	4 flats	3 flats	2 flats
Minor					7 flats	6 flats	5 flats

	F	C	G	D	A	E	B
Major	1 flat	(none)	1 sharp	2 sharps	3 sharps	4 sharps	5 sharps
Minor	4 flats	3 flats	2 flats	1 flat	(none)	1 sharp	2 sharps

	F♯	C♯	G♯	D♯	A♯	E♯	B♯
Major	6 sharps	7 sharps
Minor	3 sharps	4 sharps	5 sharps	6 sharps	7 sharps

In these tables, each entry in the top row (combined with "major" or "minor" from the left–hand column) represents a key; and in each table, the keys correspond to the "Father Charles" acronym set out above. In the first table they're the keys that start on a flat note; in the second table they start on a natural, and in the third they start on a sharp.

You can think of these as one long table, but I've split it into three so as to fit better on a web page. Notice that the entries in the "Major" row start with 7 flats (C♭ major); reading from left to right, the number of flats decreases until it reaches zero (C major), after which (still reading from left to right) each key has an increasing number of sharps, ending with 7 sharps (C♯ major). Similarly, the entries in the "Minor" row also start on the left with 7 flats (A♭ minor) and end on the right with 7 sharps (A♯ minor).

You may need to remember – particularly if you're working in the middle row – that the flats are on the left (decreasing from left to right) and the sharps are on the right (increasing from left to right). Reading from left to right, it's a bit like moving up the musical scale, one semitone at a time – but this is obviously not an exact analogy.

Just one more thing, before we move on to some examples: notice that each minor key is "three semitones flatter" than the equivalent major key. For example, F major has one flat, and F minor has four. As you get to know your way around this subject, this may come in useful if you can remember the key signature of a particular major key without having to work it out. Equally (of course), if you can remember a particular minor key, you can work out the equivalent major key by "sharpening" it by three semitones.

Example: what's the key signature of the key of D♭ major (D flat major)?

The keys that start on a flat note are in the first table. Assuming you have a pencil and paper handy, write down the letters of the acronym: F C G D A E B. We know that C♭ major (C flat major) has a key signature of 7 flats, so we can write down a 7 under the C. Moving to the right and decreasing by one flat each time, we can write a 6 under the G and a 5 under the D:

F (♭)	C (♭)	G (♭)	D (♭)	A (♭)	E (♭)	B (♭)
	7	6	5

This tells us that the key signature of D♭ major is 5 flats.

You can obviously use a similar method for the keys that start on a natural or a sharp note. The thing to remember is that C♭ major has 7 flats, C major has none, and C♯ major has 7 sharps.

Similarly, with the minor keys: A♭ minor has 7 flats, A minor has none, and A♯ minor has 7 sharps.

You will have noticed that the keys that start on a flat note only have flats (rather than sharps) and the ones that start on a sharp only have sharps. This is no coincidence, but it certainly makes life easier for the quizzer (and, I dare say, for the musician).

Example: which minor key has a key signature of 4 sharps?

If you're asked the question this way round, it's a bit more complicated because you may not know which row of the table you're on – in other words, you may not know if the key you're after starts on a natural or a sharp note. But you can use a similar technique.

Because we're looking at sharps, there's a good chance that we're going to be on the bottom (third) row; but some keys on the middle row also have sharps, so I'm going to start on the middle row.

Write down the letters of the acronym: F C G D A E B. (If you can, leave a bit of space at either end – for reasons that will soon become clear.) We know that A minor has no sharps or flats, so we're looking for the key that's four places to the right of A. This tells us that we will need to move onto the bottom row, but we can still start by writing a 0 (zero) underneath the A, a 1 under the E and a 2 under the B:

F	C	G	D	A	E	B
				0	1	2

We need to know what goes above the 4 – so we can write a 3 and a 4 to follow the 2. We then need to start writing the letters of the acronym again – F C G D A E B – except that we only need to go as far as the C, because that's what goes above the 4:

F (♯)	C (♯)	G (♯)	D (♯)	A (♯)	E (♯)	B (♯)
3	4

We now just need to remember that we're on the third row, which is keys that start on a sharp note, so the answer – the minor key that has four sharps – is C♯ minor (C sharp minor).

Example: which major key has a key signature of 3 flats?

In this case the key that we're looking for starts on a flat note, so there's a good chance that we'll need to go onto the top row.

As before, we'd start by writing down the letters of the mnemonic, but this time we're looking for a major key, so we put the zero under the C. And because we're looking for a key that starts on a flat note, we work to the left instead of to the right:

F	C	G	D	A	E	B
1	0

Clearly we do need to go onto the top row. We want to know which (major) key has three flats. So we write a 2 to the left of the 1, and a 3 to the left of the 2:

					3	2

We could write all seven letters of the acronym (F C G D A E B) in the top row of this extension to our table. But it would be quicker to use the reverse mnemonic (which, as we saw on the Music Theory page, tells us the order in which the flats are added) and write the letters down from right to left.

The reverse mnemonic is:

Battle Ends And Down Goes Charles's Father

So we write a B above the 2 and an E above the 3:

					E	B
					3	2

We're looking for a major key that starts on a flat note, so the E represents E♭ major (E flat major) – and that is our answer.

© Haydn Thompson 2017