Portfolio Theory and Currency Substitution
分析国内外货币在需求上成为替代品的条件，对比货币替代与资产替代的决定因素，指出投资组合理论中纳入外国利率等机会成本变量的依据。
ONE OF THE MAJOR REASONS Friedman (1953) and Johnson (1972) advocated flexible exchange rates was to eliminate supply side monetary substitutability, which can incapacitate domestic monetary policy. However contributors to the currency substitution literature, including Miles (1978), Girton and Roper (1981), and McKinnon (1982) have argued that when economic agents hold both domestic and foreign monies, variations in foreign interest rates or expected future exchange rates can make domestic money demand functions unstable as economic agents shift resources in response to changes in prospective relative returns. As a result, they and others have claimed that flexible exchange rates may not secure domestic monetary autonomy.l The major purpose of this paper is to demonstrate the conditions under which foreign and domestic monies are substitutes in demand, when economic agents have motives to hold both, and to contrast the determinants of currency substitutability with those of the more general concept of asset substitutability. Importantly, it is demonstrated that the usual portfolio-theoretic justification for including opportunity cost variables such as foreign interest rates, foreign inflation rates, or expected