With the development of Proposition III the main objectives we out- lined in our introductory discussion have been reached.We have in our Propositions I and II at least the foundations of a theory of the valuation of firms and shares in a world of uncertainty. We have shown, moreover,how this theory can lead to an operational definition of the cost of capital and how that concept can be used in turn as a basis for rational investment decision-makingwithin the firm. Needless to say, however, much remains to be done before the cost of capital can be put away on the shelf among the solved problems. Our approach has been that of static, partial equilibrium analysis. It has assumed among
other things a state of atomistic competition in the capital markets and an ease of access to those markets which only a relatively small (though important) group of firms even come close to possessing. These and other drastic simplifications have been necessary in order to come to grips with the problem at all. Having served their purpose they cannow be relaxed in the direction of greater realism and relevance, a task in which we hope others interested in this area will wish to share.