Now, there is one very special use for the flat and sharp symbols and that‘s to produce something called a key signature. It tells us some information about which notes we‘re going to be playing from in the piece. For the purposes of right now, we can think of a key as just being the selection of notes that a composer is telling us to play. Let‘s take a look at this group of notes.

As we can see, it uses all the different notes going from G down here, going up through what we call a scale, which is just moving up step by step through the different notes, through to C, D, E, F, and back to G again. We could use this group of notes to compose pieces of music.

But say we want to change this slightly. We don‘t want to use this particular group of notes. We want to use a group of notes that‘s very similar to this, the only difference being that we want to use an F-sharp instead of using an F in the music.

One might ask, "Why bother going through the entire piece and manually notating every F as F-sharp? Wouldn‘t musicians still understand that this piece is in the key of G major?" While this is true, there‘s a more efficient way to notate music. It‘s similar to using a keyboard shortcut on your computer. In music notation, we use something called a key signature to save time and effort.

Let‘s now enhance this simple scale by adding a key signature. Notice how the F-sharp that was previously written next to the F note has disappeared. [example] Instead, we will move it and place it at the start of the score, along with the clef and time signature. By doing so, we have established a key signature, which provides crucial information about the notes that will be utilised in this composition.

The key signature we‘ve added means that every F in this piece will be played as an F-sharp. This saves us time compared to writing a sharp symbol next to every single F in the score. However, we must remember that this rule applies throughout the entire piece. Unlike accidental symbols, which apply only to the current bar, key signatures remain in effect until the end of the composition.