I. THE BASIC MODEL
Most of our argument can be made by analysis of a very simple example. Consider an individual who will have an income of size W if he is lucky enough to avoid accident. In the event an accident occurs, his income will be only W - d. The individual can insure himself against this accident by paying to an insurance company a premium ai, in return for which he will be paid '2 if an accident occurs. Without insurance his income in the two states, "accident," "no accident," was (W W - d); with insurance it is now (W - a1, W - d + a2), where a2 = a2 - al. The vector a = (a,, a02) completely describes the insurance contract.'