The Two Faces of the Single Tax Principle

Some argue that a “single tax principle,” said to underlie tax treaties, requires that cross-border income should generally be taxed once, rather than twice or not at all. Even if one accepts this principle, it is important to recognize the difference between “upside” departures, which occur when the same dollar of income is taxed more than once, and “downside” departures, which occur when it is not taxed at all. This article argues that a focus on barring upside departures from the single tax principle can be quite misguided. While over-taxing cross-border activity, relative to that occurring in one country, may be undesirable, this should not stand in the way of letting residence countries tax foreign source income at a reduced rate, in lieu of wholly offsetting source country taxes via foreign tax credits.

As for barring downside departures from the single tax principle, such as by addressing stateless income, while this often is desirable from a given country’s unilateral national welfare standpoint (and is even more clearly worth pursuing multilaterally), the issues raised are more complicated than adherence to the single tax principle might appear to suggest.