The Problem With Synthetic a Priori Knowledge

Kant says we're uncomfortable with the idea that there should be knowledge about what's out there independently of us. And Kant agrees that such a thing is impossible. So his solution to the puzzle is to say the synthetic a priori knowledge that he's talking about isn't knowledge of what is out there independent of us. Although this knowledge doesn't consist in pure reflection on our own concept, it does nevertheless consist in pure reflections on our own concepts.