On What Matters: Volume Three by Derek Parfit
The philosophy in the book is interesting, but the writing is tedious. There is a huge summary at the start that goes into great detail. The actual work is only slightly more in depth than the summary. Much of it is in response to responses of other philosophers. I felt like I was eavesdropping on some private conversations. Much of the work discusses ethical situations and the practical applications. People are reluctant to cause harm to somebody even if it reduces harm to more people. However, people tend to be ok performing an action that has a side effect of harm. These ethics can lead to greater overall harm. (As an example, nuking 100,000 people would be considered worse than a demonstration of a powerful nuclear bomb - even if that bomb would result in 300,000 people dying of nuclear fallout.) Similarly a longer episode of military bombing is preferable to direct civilian bombing - even if more civilians die in the military bombing. People end up not being fully rational.
Other arguments get into the weeds of philosophy, such as what it means to refer to something. There is also discussions of effective altruism and efficient desire to donate to charities. Philosophy proves out some of the strange contradictions in humans.
