The secret to making music that sings is the circle of fifths. The circle of fifths is one of the foundations of musical understanding for anyone learning music theory. This includes songwriters, record producers, music arrangers, and associated music professionals.
It’s graphical
The circle of fifths is a graphical representation of how keys and chords relate to each other. To begin with, this picture shows how the 12 notes in Western music are connected.
It’s relatable
The circle helps us realize relationships between major and minor chords, as well as key signatures. Notice the connection between major keys and their relative minors (in green). In the key of C the relative minor (no sharps or flats) is A minor,
Go right
Like a clock, as we move right, each interval is a perfect fifth away from the last. For example, C, G, D, A, E, and B are all fifths apart. Following the B is F#.
Enharmonically Gb is the same pitch as F#. Following the Gb, we see Db, Ab, Eb, Bb, and F again all five intervals apart.
Go left
Another way to explain this is to start back at C once you reach B. Go back to the top of the “clock”. What interval is 5 lower than C? F is a fifth lower than C. Continuing to the left Bb is 5 intervals lower than F. Moving again to the left, Bb, then Eb, Ab, Db, and Gb complete the circle.
Key signatures
Next, let’s look at the relationships between key signatures. The key of C at the top of the clock has no sharps or flats. Moving right the key of G has one sharp, F. Right of that is the key of D with 2 sharps, F and C. Are you recognizing the pattern? As we move right we add five intervals, and one more accidental. “Accidental” is a musical word for sharps and flats. Moving right we add sharps. Moving left we add flats. Notice the Db and C# keys have the same notes. That’s what I mean by enharmonic. They share the same sound too. This is true for Gb and F# also.
Listening aid
Listening to learn about intervals and key signatures is another benefit of the circle of fifths. Remember the sound between the first words of Twinkle, Twinkle Little Star? That’s a perfect fifth. That is very helpful in learning to recognize intervals easily and apply them to other skills.
Are you interested in going deeper? Here’s a book I recommend: The Circle of Fifths: visual tools for musicians