A key is a set of notes that corresponds to a certain scale. Keys and scales provide a foundation of compatible notes that piano players use to construct melodies and harmonies. Understanding them can go a long way toward deepening your understanding of the music you play.
What does reading key signatures do for you?
It makes reading music easier because you know what notes to expect to play in each key.
It makes playing music more fun because you can start to identify what makes one song different from another if you understand the idea of songs being in a key.
It’s a tool to help you remember the music, because you can identify a certain characteristic in the context of the key. For example, if the melody begins on the third note of the major scale and you know what key you’re in, you can right away play the first note of the song.
Check out two key signatures: one for the key of G and one for the key of F. The first shows a sharp symbol on the top line of the staff, which tells you to play every F as F sharp. The G major scale contains one sharp, so this must be the key of G.
The second key signature uses a flat on the middle line of the staff, telling you to play every B as B flat. This must be the key of F because the F major scale has one flat, and that’s B flat.
You may think that only Fs on the top line are altered by the sharp in the key signature. Nope! The key signature applies to every F, not just the one on the top line. This, of course, is another time- and ink-saving decision.
The only time the same note is marked with a sharp or flat twice in a key signature is when you have two staves. In this case, you get one key signature on the treble staff and one on the bass staff.
Playing a melody with a key signature is no more difficult than playing a song without one. You just have to remember (with a little help from your friendly key signature) which notes to make sharp or flat throughout.
Here’s the opening melody to a tune called “Worried Man Blues” in the key of G. When you play, keep in mind that all the Fs are actually F sharps.
Try the same song in the key of D, which has two sharps. Notice the key signature and remember to play all the Fs as F sharps and all the Cs as C sharps.
A key signature tells you instantly which key the song is in. You may be thinking, “Well, if I have to count all the sharps or flats and then figure out which scale they’re in, that’s not very instantaneous!”
With a little experience, you’ll start to recognize the most common key signatures. Without counting, without playing — without even thinking about it really — you’ll simply glance at the key signature and know immediately which key the song is in. Most beginning piano music sticks to the key signatures with few sharps and flats or none at all.