本文使用類似於Sargent and Wallace (1982)與Smith(1988)的簡單世代交替模型來探究實質債券學說與貨幣數量學說之異同。我們同時研究這兩種學說之政策意義。本文證明以下幾種經濟情況: (1)在沒有貨幣數量學說之法律限制下,經濟社會可能會產生太陽黑子均衡;< (2)貨幣數量學說之法律限制可以用來防止太陽黑子均衡之產生;< (3)實質債券學說可以用來改善貨幣數量學說與自由銀行學說之缺失;< (4)在實質債券學說下之福利改善必須以法律限制之存在為前提。 本文同時也指出實質債券學說不同於自由銀行學說之關鍵處。 The sunspot equilibria in this paper have the characteristic that the value of currency becomes zero with some positive, but small probabilities. This meant to capture the potentiality of currency convertibility being suspended. To rule out fluctuations caused by this possibility, legal restrictions are called. Yet, the restrictions also create their own kind of inefficiency. The real-bills doctrine presents a solution to this inefficiency. Somewhat paradoxically, the prescription of the doctrine vitiates the restrictions and achieves Pareto optimality---all been done in the name of normal bank operations. This paper proceeds as follows. The basic model is presented in the second section. As SW and Smith, we first examine potential equilibria under free banking. It will be seen that not only sunspot equilibria exist, but most sunspot interpretations in Smith may be preserved in a construct that is similar to (and even simpler than) that of SW. In section III, we introduce the legal restriction that has the effect of granting the government a monopoly of note issues. The equilibria under the quantity theory regime and the real-bills regime are then studied. In section IV, we conclude the paper.