When you're learning how to play polyrhythms on piano, like "2 against 3," it's often best to just "dive in!"
Polyrhythms are tough at first. You know how play steady 8th notes, and you can also play triplets with ease. But playing 2 eighth notes in one hand at the same time you play 3 triplets in the other? Trainwreck!!!
While I generally recommend that students analyze difficult passages and play them slowly at first, I've seen the opposite approach work best with 2 against 3. Let's say you have steady quarter notes in the left hand part and you need to play quarter note triplets with your right hand.
Start by playing the LH alone. Feel the steadiness of the rhythm. Get used to the steady motion of your left arm rising and falling with the pulse. Imagine your right arm doing something different without disturbing the steadiness of your left arm. Then stop playing for a moment and sing the quarter note triplet rhythm. Sing it while keeping a quarter note pulse with your foot on the ground. Once you can do this with ease (and yes, it might take a while), play the left hand part again until it becomes automatic and solid again.
When you're ready, try playing the quarter note triplets against the steady quarter notes of the left hand. You'll be playing 3 notes with your RH in the same amount of time that your LH plays 2 quarter notes. I think of quarter note triplets as being kind of like 8th notes that are stretched a little, like taffy or chewing gum. P-u-l-l-e-d and s-t-r-e-t-c-h-e-d.
Yes, you'll mess up. Yes, the rhythm will fall apart. Yes, you'll get frustrated at first. But this is a stage that HAS to happen in order to master it. Think of yourself as a young child learning how to walk. They fall down a lot but they never give up. And then one day, they get it.
You'll get it too. Don't give up.
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