EXCERPT 1

There are many applications in the "real world" for this technique. Below are a couple of common examples:

1. If you walked into a room and a friend was playing a song or melody on an instrument, you could play one note on your instrument and instantly know what key he or she was playing in. Armed with that information you could start improvising in that key, or just playing along with them in the right key.

2. If someone played a chord progression that changed keys and you were asked to improvise over it, you would be able to listen to the notes you play and follow the key changes. For example: a chord progression might start in Ab, you would play a C, it would sound like the 3rd so you could improvise in Ab. Then you might come back to your C a few bars later and notice that it now sounded like the 6th; this would tell you that you have now modulated to Eb so you would start improvising in Eb.