傳統的租稅理論忽略了商品的消費具有不可分割的性質, 有鑑於此, 本文在此一背景下探討柏瑞圖效率的租稅結構。文中發現: 在滿足 柏瑞圖效率的租稅結構下,高(低)能力者的邊際稅率除了與課稅後 不可分割財的消費型態有關外,同時也取決於低(高)能力者的自我 選擇限制式以及高(低) 能力者的工資門檻限制式是否會受限。因 而在稅後高能力者會購買不可分割財的前提下,即使低能力者的自 我選擇限制式不會受限, 只要高能力者的工資門檻會受限, 則高能 力者面對的邊際稅率將為負, 而不是0, 其原因在於, 受限於不可分 割財消費門檻之限制, 租稅組合中對高能力者固定稅額之課徵, 無 法使得其所得淨社會邊際效用水準等於1; 在維持稅收不變的前提 下, 相對於傳統高能力者邊際稅率為0的解, 透過高能力者的邊際 稅率之降低, 並增加固定稅額的課徵, 可以放寬高能力者的門檻限 制式, 讓其所得淨社會邊際效用水準更貼近於1。

Traditional literature neglects the impact of indivisibility of goods on the design of optimal income taxation. For this reason, this paper sets up a model based on Stiglitz (1982) with two different kinds of goods: one is the traditional consumption good and the other is the so called indivisible good. It is shown that under the Pareto efficient tax structure, the marginal tax rates on the high (low) ability taxpayers depend not only on the patterns of indivisible goods, but also on whether low (high) ability taxpayers’ selfselection and high (low) ability taxpayers’ wage threshold constraints are binding. Under the premise that high ability taxpayers will always purchase indivisible goods and the constraints of their wage threshold are binding, the marginal tax rates should be negative rather than zero on the high ability taxpayers, even that the low ability taxpayers’ self-selection constraints are not binding. This result is different from traditional models which show that the optimal marginal tax rates on high ability taxpayers are zero. The reason is: being constrained to the wage threshold, lump-sum taxation levied on high ability taxpayers cannot make the net social marginal utility level equal to 1. Hence, reducing marginal tax rates and increasing lump-sum taxes on the high ability taxpayers can make the level of net social marginal utility closer to 1 and thereby improve social efficiency.