The choices we make today have consequences for what life will be like for future people, how many future people there will be, and who those future people are. Such
quality, quantity
, and
identity
issues – and more besides – fall within the domain of
population ethics
. A widely accepted goal within moral philosophy is the design of a moral theory that plausibly instructs whether an agent's choice to distribute well‐being across a given population in a given way is morally permissible in light of alternative distributions of well‐being across that same population available to that agent at the critical time. Closely related is the design of a theory that plausibly ranks one such distribution against another in terms of the respective moral value, or degree of goodness, of each. The recognition that drives population ethics is that any adequate moral theory must also take into account that the very choices under evaluation for their permissibility may themselves produce distinct populations – some larger, some smaller, some that overlap in terms of identities of their membership, and some that do not. An adequate moral theory must give a plausible account, in other words, of both “Same People” (and hence “Same Number”) cases and “Different People” (whether “Same Number” or not) cases (Parfit 1987: 356, 351–454; Blackorby et al. 1997, 2005).