Combined Contributions in Portfolio Theory

Finance theory had been slow to develop until a dramatic explosion in results occurred over just a handful of years. Before 1937, there had been a gradual evolution in our understanding of the significance of the interest rate. Irving Fisher had given finance theory the tools to understand why people save. John Burr Williams had created the present value approach to the pricing of securities based on their expected future profits. Meanwhile, John Maynard Keynes, the financier turned macroeconomist, demonstrated to the literature that our financial portfolio contains not one generic asset, but rather many assets, with the share we keep in each is dependent on such things as income, interest rates, and overall market perceptions. Finally, in the late 1940s and early 1950s, we began to gain a better understanding of how our savings decisions evolved over our life cycle through the works of Franco Modigliani, Richard Brumberg, and Milton Friedman.