What is a key? Every song has a key, and that key is defined by the notes and the chords used in the song. You can often work out the key of track by just singing or playing one note. When you find the right note, you’ll find it pretty much fits throughout the whole track, and it feels as though the song is really solid when it returns. Its going to depend somewhat on whether the song changes key at any point, but try it out with some tracks, and find which note fits the best, and that note will commonly be the “key” of the song. Many commerical tracks actually stay in one key and should be fairly easy to work out.
If we take the chords that we used in our previous tutorial on chord progressions, you will notice that all the notes that are used in all of the chords can be found in the scale of C Major. In that case, we can say with some confidence that we are playing chords that belong in the key of C Major.
If we then hum a tune over the top of these chords, say ‘Blue Moon’, we can say once and for all that we are in the key of C Major. No argument. The key in a piece of music identifies the tonic triad (which is always the chord that shares the same note name as the key), major or minor, which represents the final point of rest for either the complete song, or the focal point of a section of that song.
Why do keys matter? It’s very handy to know which key you’re in when writing a song. For example, you’ll notice when you play the ‘Blue Moon’ chord sequence that when you play the C Major chord again as you go round the sequence there is a nice feeling of resolution, a certain rightness to it. The main reason for this is that we are in the key of C Major, and C Major is the tonic triad chord of the key. That is how we can say that we are playing a chord sequence in the key of C Major. Also, there are certain triads that are available within a key, giving you a simple harmonic flow when you use them in a chord sequence.
For example, in a major key there are six major & minor triads you can use. If we stay with C Major as our key for the moment, they are:
|C major||D minor|
|E minor||F major|
|G major||A minor|
Notice that in all these chords, you only need to play white notes. As the key of C Major includes every white note and none of the black notes, we can say that all of these chords are available to us in the key of C Major. Similarly, these same six chords are available to us in the key of A minor as the key of A minor includes every white note and none of the black ones.
As you may have imagined, seeing as they use exactly the same notes, the keys of C Major and A Minor have a special relationship with each other: A Minor is the Relative Minor key of C Major. Similarly, C Major is the Relative Major key of A Minor.