A centuries-old debate about the ethics of future generations may be drawing to a close, but its conclusions raise as many questions as they answer

""Like my cat, I often simply do what I want to do." This was the opening sentence of Derek Parfit's philosophical masterpiece, Reasons and Persons. He believed that it was the best way to begin his book because it showed something important about people. Often we are not as special as we think we are. For instance, when people simply do what they want to do they appear to be utilizing no ability that only people have. On the other hand, when we respond to reasons, we are doing something uniquely human, because only people can act in this way. Cats are notorious for doing what they want to do, and the sense of proximity between a cat and its owner pleasingly heightens our sense of their similarity. Hence, there could be no better way for this book to begin.

However, there was a problem. Derek did not, in fact, own a cat. Nor did he wish to become a cat owner, as he would rather spend his time taking photographs and doing philosophy. On the other hand, the sentence would clearly be better if it was true. To resolve this problem Derek drew up a legal agreement with his sister, who did own a cat, to the effect that he would take legal possession of the cat while she would continue living with it.

Reasons and Persons was far from being Derek's final word on the philosophical problems that had consumed him for the previous 17 years. Indeed, it has been said that Derek only agreed to publish it under pressure from All Souls College who were threatening not to renew his fellowship, and he insisted the publisher accept it in 154 individual instalments so that he could submit each one at the last possible moment, mere days before the book went to press. Yet, the book has become one of the most influential, and heavily cited, works of philosophy published since the Second World War. It consists of four sections, each of which considers a different set of arguments for why people matter less than we might suppose, and why our reasons for action might be otherwise than they seem."