John C. Harsanyi is a Hungarian-American game theorist (1920–2000). Prior to TJ, Harsanyi (1953) appeals to rational choice in a hypothetical situation similar to Rawls’s original position in order to justify a principle that governs the basic structure of society. He contends that average utilitarianism would be rationally chosen. Harsanyi (1955) attempts to establish average utilitarianism through two theorems. The Aggregation Theorem holds that if (1) individual and social preferences satisfy the expected utility axioms and are represented by the von Neumann-Morgenstern utility function and (2) a Pareto principle is satisied, then the social utility is a weighted sum of individual utilities. This theorem allows for different weights to individual utilities. The Impartial Observer Theorem introduces a hypothetical observer who is sympathetic to, but impartial amongst, individual preferences. Given that this impartial observer does not know who will occupy a particular actual position, he would judge that there is an equal chance of being any member of society. As such, the Impartial Observer Theorem holds that the weight given to each individual’s utilities must be I/n in an n-person society. From these two theorems, Harsanyi concludes that it is rational to prefer the principle that would maximize average expected utility.