The Valid Core of Rationality Hypotheses In the Theory of Expectations
梳理理性预期假说的背景与核心命题，指出其需要四种限定条件，并论证在限定后仍保留的实质内容可称为可信性假说，对研究预期与政策效果的经济学者有参考价值。
SECTION 1 DESCRIBES THE BACKGROUND of the debate from which the recent literature on expectations has emerged, and section 2 summarizes the salient features of the most ambitious version the hard-line version-of the rational-expectations hypothesis. This version will be interpreted as including two general propositions, one of which distinguishes sharply between the effects of the systematic and those of the stochastic components of demand policy, and the other of which denies the effectiveness of demand policies directed at the real variables of the economy. Following the formulation of these two propositions in section 2, sections 3 through 6 describe four qualifications of the propositionsessentially four classes or types of qualiScation that I believe need to be stressed. Several authors usually associated with rational expectations theory have recognized the validity of some of these, but no reasonably comprehensive discussion has so far been presented of the qualifications that I regard as essential even in a first approximation to reality. Hence, no analysis has been developed of what remains after allowance for these qualifications or limitations. I suggest that quite a bit of substance does indeed remain, and that we are left essentially with what in other writings I suggested calling the credibility hypothesis. The reason why that hypothesis may be so referred to is that it places the emphasis on the difference between