Understanding keys and key signatures

This section is all about musical keys and key signatures: we will learn how they are made and why we need to use them.

If you are new to music theory, you might find this material a little complicated at first, so be prepared to go slowly and make sure you understand each concept before you go on to the next part. It is important that you learn to recognise the different sounds that are discussed, so listen carefully to the sound clips.

When we look at a piano keyboard, we see white notes and black notes. The keyboard, and musical notes in general, are organised in a repeating pattern as follows, starting with the first black note on the left of the picture:

Then the pattern starts again from C#.

Arrangement of notes on piano keyboard

As we play notes from left to right along the keyboard, we hear that the pitch gets higher. The difference between two pitches is called an interval.

When we play two white notes that have a black note between them, such as C and D, the interval we hear is called a whole step, or tone. Listen to this clip of notes going up and down by a tone:

When we play two white notes that do not have a black note between them (namely E and F, or B and C) or we play a white note and an adjacent black note, the interval we hear is called a half step, or semitone. A semitone is the smallest musical interval we can play on a piano - other instruments such as a trombone or guitar can play smaller intervals by moving the slide slightly or bending a string. Listen to this clip to hear notes going up and down by a semitone:

If you're not familiar with tones and semitones, listen again to the two clips above until you can hear the difference very clearly - this is a fundamental part of music theory and it is even more important to recognise these different sounds than it is to understand the concepts.

We can play lots of simple tunes, such as "Happy Birthday To You", "My Bonnie Lies Over the Ocean", or "Michael Row the Boat Ashore" using just the white notes. If you try this on a piano, you will find that many of these simple tunes, when played only on the white notes, end on the note C, which gives them a satisfying, finished sound. When we play these tunes using just the white notes, we are playing in the key of C major, and the note C is called the tonic. (There are some tunes which can be played only on the white notes which are in other keys - these need not concern us for the moment. There are also plenty of tunes that do not end on the tonic.)

If we start at C and play the white notes going up the keyboard until we get to the next C note, we hear the familiar sequence do-re-mi-fa-so-la-ti-do. Click the play button to hear it:

Here it is in music manuscript notation:

This is called an ascending C major scale - the word scale comes from the Italian word "scala" meaning "ladder" - a scale is something we can go up (or down) one note at a time, just like we can go up or down a ladder one rung at a time. Starting at C and going down the white notes until we get to C again is called a descending C major scale, which sounds like this:

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Here is the music notation for a descending C major scale:

The first eight notes of the Christmas carol "Joy to the World" form a descending major scale:

The same is true of the Irish tune "Garryowen":

Starting our major scale from C, the next C we play is the eighth note in the series, so the interval from one C to the next is called an octave. We can play our major scale ascending or descending for more than one octave, depending on the range of the instrument.

In the next page, we will start to find out how we can make major scales starting from notes other than C.