The behavioural economist and the social planner: To whom should behavioural welfare economics be addressed?

This paper compares two alternative answers to the question 'Who is the addressee of welfare economics?' These answers correspond with different understandings of the status of the normative conclusions of welfare economics and have different implications for how welfare economics should be adapted in the light of the findings of behavioural economics. The conventional welfarist answer is that welfare economics is addressed to a 'social planner', whose objective is to maximize the overall well-being of society; the planner is imagined as a benevolent despot, receptive to the economist's advice. The alternative contractarian answer is that welfare economics is addressed to individuals who are seeking mutually beneficial agreements; a contractarian recommendation has the form 'It is in the interests of each of you separately that all of you together agree to do x'. Each of these answers should be understood as a literary convention that uses a highly simplified model of politics. I defend the contractarian approach and show that it is less supportive of 'soft paternalism' than is the welfarist approach.