This chapter starts to consider how wellbeing can be aggregated across a distribution. It describes two possible route to aggregation, called ‘the people route’ and the ‘snapshot route’. Each relies on a particular assumption of separability, which the chapter explains. The chapter examines the credibility of separability of times. It shows how separability of times conflicts with the value of longevity, and concludes that this principle cannot be relied on. It therefore rejects the snapshot route to aggregation.
Keywords: separability, snapshot valuation, intertemporal aggregation, interpersonal aggregation, value of longevity,