 We can distinguish bargaining from aggregation models of agreement. Rather than seeking an outcome that (as, roughly, the Kalai-Smorodinsky solution does) splits the difference between various claims, we might seek to aggregate the individual rankings into an overall social choice. Arrow’s theorem and related problems with social choice rules casts doubt on any claim that one specific way of aggregating is uniquely rational: all have their shortcomings (Gaus and Thrasher 2021, chap. 8). Harsanyi (1977, chaps. 1 and 2; 1982) develops a contractual theory much like Rawls’s using this approach. In Harsanyi’s approach, reasoning behind a veil of ignorance in which people do not know their post-contract identities, he supposes that rational contractors will assume it is equally probable that they will be any specific person. Moreover, he argues that contractors can agree on interpersonal utility comparisons, and so they will opt for a contract that aggregates utility at the highest average (see also Mueller 2003, chap. 26). This, of course, depends on the supposition that there is a non-controversial metric that allows us to aggregate the parties’ utility functions. Binmore (2005) follows Harsanyi and Amartya Sen (2009, Chap. 13) in arguing that interpersonal comparisons can be made for the purposes of aggregation, at least some of the time. John Broome (1995) develops something like Harsanyi’s approach that relies on making interpersonal comparisons.