A key is a structural device of music. It is derived from a major or minor scale, which in turn creates the chords that belong to that key. In terms of our experience of music, keys are a fundamental aspect of the way we hear and organise it in our minds. A key is a tonal center, with the key note and key chord at its core. Whenever we land on the key chord (chord I), it feels as though we have reached “home”, or the center of the music or, to use a physical analogy, regained our balance. In a major key, this is usually a satisfactory, secure place to be; in a minor key, it will feel sadder.

Even within one key, the progression of chords represents a departure from the center. To use a geographical metaphor, the chords within a key are like the different districts of your home town, with happy and sad associations.Changing the chord within a key is like making a short journey. By analogy, a key change is like a visit to another county or state, which could be nearby and therefore have similar terrain, or distant and have a very different landscape. A key change is called a “modulation”.