In the key of C major or C minor you can get two most of the other 12 keys simply by morphing using an augmented chord. For the remaining three keys you have to do some extra morphing using the augmented chord. For those three keys you can use a diminished chord to morph more quickly.
This allows you to freely move around in all 12 keys using morphing.
The morphing principle simply means that you always use half tones in your movements. No whole tones. It is obviously not the only way to modulate, but it is the most effective way to add variation to your music because this kind of movement tends to be very subtle. I call the augmented and diminished chords the “grease of harmony”.
These slippery chords allow us to be sneaky.
They allow us to move around in a way that fools our listeners, because we keep getting to new and interesting places, yet how we do that is very difficult to analyze or figure out in any way.