Keys

Scales and chords in music can be played in one of 12 keys - one for each of the twelve notes, in either a major or minor form. So what does that mean?

Take the major scale for example. The major scale is defined by the following intervals (where each interval is a whole step / tone (W) or a half step / semi-tone (H)): W - W - H - W - W - W - H. But this major scale can be played in any key, as defined by a root note (its tonic) that could be any of the 12 notes - A, A#/Bb, B, C, C#/Db, D, D#/Eb, E, F, F#/Gb, G, G#/Ab. In all cases the intervals stay the same, but the root note changes. The scale has the same emotional feel but at a different pitch.

The same is true of chords. Chord shapes as defined by their intervals can be repeated in different keys and will sound like the same kind of chord, again just higher or lower in pitch.

A key can be thought of as a family of notes and chords that sound natural, stable and satisfying when played together. As an analogy, a key is like a colour palette in painting - Other colours exist outside of the palette, and you might have reason to stray outside of the palette from time to time, but sticking to a 'home' set of colours would provide a feeling of coherence to a painting.

Of course, the same notes can belong to multiple keys, and if we are to infer a key from the notes played, we need enough of them to determine the key. That the notes outside of a key might still be used make this a best effort determination. Our brains will interpret a key based on the context of notes around the tonic and infer where the 'gravity' of a melody feels like it wants to resolve - This is the key. Notes that sit outside the key feel the most unresolved of all, but even notes within it can pull strongly back towards home.

Try it: work out the key from the notes

The tool below can be used to 'detect' the key for a given set of notes. Rather than picking a key and reading off its notes, we can do the reverse - click the notes you hear and watch it narrow down which keys they could belong to. This is designed to help you see and feel what a key really is.

1. Click the notes on the keyboard. You'll see each one light up and play a sound.
2. Watch the list of possible keys narrow. A key remains a candidate only while it contains every note you have clicked. The more notes you add, the fewer keys remain.
3. Notice you can never reach a single key. Every major key shares its seven notes with its relative minor - its partner on the same row - so the notes alone can only narrow you to a pair, such as C major and A minor.
4. Press "Resolve to home (tonic)" to settle the pair by ear. It plays a few notes that lean towards home, pauses, then lands on the home note - the tonic - which flashes on the keyboard. Select either the major or minor key in a surviving pair to hear the same notes pulled towards a different home.

That is the heart of what a key is: a family of notes that belong together, with one note that feels like home. And if you click notes that do not all fit any single key, you will see "No key fits" - a sign that at least one of them sits outside the key (a note we would call chromatic).

Typically, the composer of a piece of music will tell you the key, by displaying the key signature after the treble / bass clef on the staff. The key signature is indicated using sharp or flat symbols on the relevant note lines / spaces on the staff to indicate which notes are played using a sharp or flat note, and from this we know what the key is. Note that a sharp or flat on a specific line or space on the stave / staff applies globally for that note name across all octaves of the instrument. Where a note in a piece varies from the sharp or flat indicated by a key signature, the natural symbol will be used to temporarily cancel the sharp or flat denoted by the key signature.

Some example key signatures:

Why would we choose a specific key?

To the listener, changing key does not affect the emotional feel of the music, just the pitch as we have already noted. So why not play everything in the same key?

One reason is because of vocal or instrument ranges. A singer's vocal range might be limited such that it might crack on high notes on one key, but another key might match the singers natural range better. The same might be true for an instrument, one key might fit more with an instruments natural physical range. The notes of a melody in one key might be easier to play, for example another key might force a pianist to use more black keys or a guitarist to bar their fingers across the fret board more.

Another reason is that instruments have different resonances and textures, the sound of a melody in one key might sound better.

By contrast, modulation (changing keys within the same song) can be used to change the energy felt in a song by making it sound brighter for example.