Circle of 4ths / 5ths
The circle of fifths is one of the most powerful tools in music. A group of notes make a chord. A group of chords make up what's called chord progressions. Chord progresssions are used to form songs. Its important to learn the circle of 5ths because most songs use portions of the circle's chord progressions within its structure. For example, here is a portion of the popular song "Brown eyed Girl" :
|G | C | G | D |
If you compare the chord chart to the diagram above you will notice that this song uses (2) progressions from the chart. G -->C and G -->D
Overall, this chart represents what's been proven to sound good to our ears. Start at the C and play a Major C chord. Their is a natural tug to your ear to want to play the G chord or maybe the F major chord. Both sound great! Some songs only use small sections of the "Circle." Other songs, like "Fly me to the moon", use large portions of it. Below is an audio example of playing the "circle" using triads. In addition, their is sheet music attached so that you will be able to visually see whats going on.