对富人增税是否会抑制经济增长，延缓复苏？这取决于富人在增税后的行为态度。若税后收入缩水，他们是否会因此减少工作量？将家产移至海外？抑或更多地通过赋税较低的形式获取收入？为了解答上述问题，经济学家对过去诸多税率政策变化的收效作出研究。

　　Martin Feldstein, a Harvard economist, found that the taxable income of the rich adjusted dollar-for-dollar with tax rates when America cut its highest tax rate from 50% to 28% in 1986, so that tax revenues stayed the same. This would suggest that raising top tax rates is likely to produce little extra revenue, while distorting economic behaviour further. But others have found that this adjustment in taxable income is driven largely by people altering when and how they take their income in order to minimise their tax burden. For instance, there was a big fall in taxable income after tax rates rose in 1993; but most of this seems to have come from a few rich people hurrying to cash in their stock options before taxes rose.

　　哈佛经济学家马丁·费尔德斯坦指出，1986年美国将税率上限由50％下调至28％，与之相应的富人应税收入也作出等额调整，总税收与往年持平。这就意味着提高税率上限可能不会带来多少额外收益，反倒进一步扭曲经济行为。但是，还有一些经济学家认为，对应税收入的调整主要是应富人的需求--他们通过调整获取收入的时间与方式，使赋税达到最低。举例来说，1993年税率上升后，应税收入大幅下降；这很大程度上是因为一些富人此前赶着在税率调高前兑现股票期权。

　　Thomas Piketty of the Paris School of Economics, Emmanuel Saez of the University of California, Berkeley, and Stefanie Stantcheva of MIT argue in a new paper that this is why few studies have been able to show any significant long-term effect from raising top tax rates. But such avoidance, they say, is merely a symptom of a poorly designed tax system. It is silly to have a high tax rate while simultaneously giving people many ways to avoid paying it. So the first task of tax reformers must be to minimise such opportunities by having a broader tax base, better enforcement and similar tax rates for different kinds of income.

　　巴黎经济学院的托马斯·皮凯迪，加州大学伯克利分校的伊曼纽尔·赛斯和麻省理工的斯蒂芬妮·斯坦特切娃在最新发表的论文中谈到，正是由于富人对税后利益最大化的需求导致对应税收入的调整，使得至今鲜有研究表明提高税率上限会造成任何深远影响。但他们也认为，富人的避税行径不过是税制系统设计糟糕的表现。设置高税率的同时提供诸多避开它的方法，不可谓不愚蠢。因此，税制改革者的首要任务务必是使避税之人毫无可乘之机。手段包括：扩大税基，加强管制，对不同形式的收入设置相当的税率。

　　That is relatively uncontroversial. But their other finding is likely to raise a few eyebrows. They reckon that if the tax system were reformed to make evasion impossible, the top tax rate might be able to rise to as much as 83%—that is, to levels last seen in the 1960s—without hurting the economy. This is because people do not seem greatly to adjust how much they work when tax rates change. Higher top rates may also discourage big earners from spending too much of their time trying to bargain for a larger share of the overall pie.

　　前述相对来说争议不大。但他们的另一个研究结果可能会让人狐疑好一阵子。据这些专家估计，若改革后的税制要完全杜绝避税，税率上限可以调高至83％（上一次出现如此高的税率还在20世纪60年代）都不会阻碍经济发展，因为人们不大可能在税率变化后调整工作量。面对更高的税率，富人也不会再花大力气分一杯更大的羹。

　　Now all that remains is to remove the loopholes. On past experience, America’s rich need not lose sleep over that.

　　现在剩下要做的是堵住法律漏洞。从以往的 经验看，富人们无须失眠。