“Decision theory posits that rational agents attach different amounts of value, or “utility,” to different things that might happen, and then prefer to maximize the expected amount of utility—the average of all the possible outcomes, weighted by their probabilities. Given two outcomes A and B, an agent that assigns exactly twice the utility to B as to A should be indifferent between A happening with certainty and B happening with 50 percent probability. There are a bunch of reasonable-sounding axioms that any good assignment of utilities should obey; for example, if an agent prefers A to B and also prefers B to C, they should definitely prefer A to C. Anyone who goes through life violating the axioms of decision theory is deemed to be irrational, and that’s that.”