Economics stresses the core idea of gains from trade. Yet in many circumstances, not everyone approves of gains from trade, mostly for ethical reasons. Not everyone thinks that kidneys should be bought and sold and not everyone thinks that pollution should be exported to poor countries. Intuitions about fairness, equitable treatment, distribution, and other matters often clash with the economic notion of increasing gains from trade.

We respect the distinction between positive economics—predicting what will happen—and normative judgments—what should be done. So we haven’t tried to answer these ethical dilemmas or give you our sense of the best possible ethical theory. But we do know that if you want to understand and participate in debates about economic policy in the real world, then you must also have some understanding of different ethical theories and their foundations.