You know, there are books out there for when you want to read Kant but not by Kant. That said, my general approach for reading a non-fiction book and really understanding it is the following: - Highlight new things I learn with yellow (physical book: underline) - Highlight key arguments with purple (physical book: underline + exclamation mark) - After having read and highlighted the entire book, write down / copy the core arguments from the purple notes. If I did it right, I can tell the entire story of the book with just those notes, filling in the gaps with common sense or logical thinking. If I want to re-read the book, I only have to care about the purple highlights. If I'm looking for interesting tidbits or supportive arguments, I look at the yellow highlights.