Tax progressivity is often at odds with efficiency.

at odds with 教你一招 可译为“与...想牴牾” 改译：累进税往往同高效率相牴牾。

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To explain why, let us start with the premise that the defenders of any progressive tax have to give some principled account of the optimal degree of tax progressivity.

我们的前提假设是：累进税的支持者必须要对最优累进率给出有力的解释。

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In practice progressivity has tended to imply more than one rate of tax, for instance, which is necessarily less simple than a flat tax rate.

事实上，累进税意味着不仅仅只有一个税率。例如，累进税一定没有固定统一税率那么简单。

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Agree on specific revenue-raisers while maintaining or improving tax progressivity.

FORBES: Is The GOP Tax Reform Strategy A Fiscal Trap?

Lots of things are important when it comes to stock performance, and unfortunately a rather disturbingly high number of them are generally ignored by most investment analysts: religion (yes, religion), fertility, ethical corruption, moral corruption, property rights, soundness of currency, debt, tax progressivity, and size of government (which is another topic on which Mr. Mauldin has become a little muddled: more on this later).

FORBES: John Mauldin's Muddled Stock Return Model

In other words, tax share says nothing at all about the progressivity of tax rates.

FORBES: How Progressive is the American Tax Code?