There is one common thread that runs through all three of these challenges. It is a plea to look beyond the standard model of taxation in which it is assumed that the taxed goods directly enter into individuals' utility functions or firms' production functions. At a very basic level this assumption is incorrect because what is taxed is what the taxpayer reports or the tax agency observes, not what the taxpayer consumes or the firm uses and produces. Thus we must analyze tax systems in which the compliance and enforcement elements are explicit.
This focus is especially important for international taxation issues because of the difficulty of taxing nonresidents' income and the foreign-source income of domestic residents. It is inevitable that tax systems are designed with these practical difficulties in mind, and, in order to participate fully in the policy debates, economists ought to think carefully about these issues.
The distinction may also hold the key to making sense of the empirical evidence about the impact of the U. S. tax changes of the 1980s. There are many avenues of response to tax rate changes other than changing one's consumption bundle or input mix; we need to think hard about whether these responses preclude or merely accompany the “real” responses that are of ultimate interest.
If public finance is to decline in the 1990s, it will not be because of a lack of intellectually exciting challenges that confront us. There are many such challenges, and I am confident that they will attract the attention of both newly minted and well circulated economists.