So what does the circle do for us? It gives us a scheme by which we can be as musical as possible. For example, I was surprised to learn that many DJs at clubs use the circle when programming their sets. They learn the keys of all the songs they want to use and arrange them using the circle.

For example, if a song is in the key of C major, it can be followed up with one in G major or F major. What this does is allows one song to segue into another without a radical change in key. Not only does it sound superior to a DJ whose set is not arranged in keys, but it won't break the groove of the dancers. The DJ wants to keep them on a the floor as long as possible. He sets up a groove with a certain key and beat. He then segues into another song by matching the key and the beat but not in a boring way. Something in C major at 80 beats minute should not be followed up with something else in C major at 80 beats a minute. Maybe segue into something at 160 beats a minute in G major. The two beats are related (80 x 2 = 160) and so are the keys. Why? Because G major is a fifth away from C major and therefore has a relationship to it. This holds the dancers in the groove and keeps them dancing which keeps them in the club which keeps them buying drinks, etc. A DJ who breaks the spell with songs that are out of key with one another and/or with ill-matched beats causes dancers to leave the floor and possibly the club.

DJs say that you can even use the equivalent minors and get away with it--go from C to A, or C to D (the minor of F major) for example. Basically go around the circle link-by-link and program your set that way and you will became a sought-after DJ who knows how to get and keep people dancing. You don't want to jump from C to Eb for example because that might break the spell by changing key too radically. If the current tune is in Eb then go to Ab next or Db or B (B being the minor equivalent of Db).

Basically, if the seguing key is a fourth or fifth away from the current song and the beat is close, you can jump to it seamlessly and keep your crowd entertained.