A key signature is like a fingerprint for a key. It identifies a key as being different from all other keys. Key signatures are expressed as a collection of sharps and flats. For example, the key signature for the key of C is “no sharps or flats” because the notes in the key (and the C major scale) are just the natural notes C, D, E, F, G, A, and B. The key signature for the key of D is “two sharps, F♯ and C♯.” Why is that the key signature? You’ll learn that later in this chapter. For now, just understand that a key signature is simply a list of sharps and flats in a certain key. You actually played through all the keys in the last chapter when you played all 12 scales.

Memorize This

  • A key signature tells you how many sharps and flats there are in a key and thus a scale
  • Because there are 12 major scales, there are 12 major keys – each of which has a unique key signature
  • The key of C major has no sharps or flats

Mixing Sharps and Flats

Major scales never have both sharps and flats. The key signature for any major scale will have just flats, just sharps, or none (as with the key of C). Also, every major scale has a different number of sharps and flats. For example, only one major scale has one sharp, only one major scale has two sharps, only one major scale has one flat, etc.

Memorize This

For all major scales:

  • A key signature has either sharps or flats – never both
  • A key signature will never have two of the same thing – like two F♯s
  • Every key signature has a different number of sharps and flats

Writing Key Signatures

To properly write out a key signature, you need to know a little about reading music. We’ll learn how to do that later. For now, we’ll simply write out key signatures as a list of sharps or flats.

Once you know how to read music, you’ll be able to read this key signature and tell it’s the key of D.

For now, we can simply write the key signature for D major like this:
F♯ C♯
or we can write out all of the notes in the key as a chart, like this:
D E F♯ G A B C♯ D

Don’t worry if you don’t know why the key of D major has an F♯ and a C♯. You haven’t learned that yet. That’s what the rest of this chapter is about! In the next lessons, you’ll learn how to figure out the key signature for every major key and write it out as a chart.

Key Signature Order

When writing the sharps and flats of a key signature, they should be written in the correct order. For example, in the key of D major:
F♯ C♯ is correct while
C♯ F♯ is incorrect.

This has to do with the way in which the sharps and flats are arranged in written music like this:

I’ll show you the orders now, but don’t worry about memorizing them. I’ll put them here just to satisfy your curiosity. Why the order matters is something we’ll get to much later in a different chapter when you start reading music.

Order of Sharps

  • F♯ C♯ G♯ D♯ A♯ E♯ B♯
  • Just remember the first letter of each word in the sentence Fat Cats Go Down Alleys Eating Birds
  • Sharps are in the opposite order of flats

Order of Flats

  • B♭ E♭ A♭ D♭ G♭ C♭ F♭
  • Remember the word BEAD followed by the phrase Go Catch Fish. Or if you’re a math person, Greatest Common Factor.
  • Flats are in the opposite order of sharps

Check Yourself

Based on the list of sharps and flats, identify each as being a valid key signature for a major scale or not.