There are other ways in which, if people understand and think about object-given value-based reasons, things would go better. As Keynes remarked, many politicians act in ways that show them to be slaves of some dead economist. Many economists, we can add, think in ways that show them to be the slaves of some dead philosopher. Like most of the sciences, economics grew out of philosophy. When welfare economics began in the late nineteenth century, economists knew that wealth is only imperfectly correlated with happiness, and that, of these two, it is happiness that matters. For much of the twentieth century, economists forgot these truths. Many economists even believed that interpersonal comparisons of well-being make no sense. Many also believed that, in their professional work, they should be concerned only with facts, not values. Remember the remark: ‘That’s not a value judgment. Everyone accepts it.’ Economists are not chiefly to blame for having these beliefs, since it was philosophers who first claimed that reasons are given only by desires, that all rationality is instrumental, and that no values are facts, because there are no normative truths. Given our increasing powers to destroy or damage the conditions of life on earth, we need to lose these beliefs. It is not wealth that matters, or mere preference-fulfillment, but happiness, justice, and the other things that make our lives worth living.
Derek Parfit, On What Matters, p. 462-463