In this post I will briefly talk about a concept that’s very important to know in order to easily play songs in all 12 keys. It’s called the Number System.
Before learning the Number System, I used to find it quite challenging to transpose songs since I thought of each key as its own distinct set of notes. But by thinking of the tones of a scale as numbers, you create a common language to describe what you need to play regardless of scale. This made it significantly easier for me to play in all 12 keys. Here’s a quick example. Suppose you want to play the melody of the first line of Mary has a Little Lamb in the key of C, one can describe this as
E D C D E E E
In the key of G, it will be:
B A G A B B B
Now, instead of thinking of the tones distinctly when trying to play the song, we can use the Number System to abstract this to
3 2 1 2 3 3 3
To make this system effective, one will need to know for each key what tone corresponds to what number. E.g. C is the first tone of C, D is the second tone of C, etc. Once you master the Number System, you can apply it to chord progressions to quickly understand common patterns in music, e.g. the 2-5-1 or 7-3-6 chord progressions.