The Supreme Court's decisions delineating the constitutional limitations on state tax power have often defied rational analysis. The Court read the commerce clause as forbidding a state tax on the privilege of doing interstate business but not on the privilege of doing interstate business in corporate form. It construed the import-export clause as prohibiting a state tax on bales of imported hemp awaiting use in manufacturing but not on piles of imported ore and plywood awaiting such use. It interpreted the supremacy clause as barring a state tax upon the sale of goods to one government contractor but not to another because the second was not deemed to be a purchasing agent for the federal government, even though in both instances the federal government bore the economic burden of the tax and ultimately took title to the goods. Indeed, the Court itself came to recognize that consistency was not the hallmark of its pronouncements in this field, that form occasionally prevailed over substance, and that "[t]o attempt to harmonize all that has been said in the past would neither clarify what has gone before nor guide the future."

In light of the difficulties in generalizing about the Court's precedents regarding particular constitutional limitations on state tax power, generalizations embracing decisions directed to several separate limitations are especially suspect since they aggravate the danger of oversimplifying problems that have been resolved for years on the basis of razor-thin factual distinctions and ephemeral doctrinal nuances. Nevertheless, with due regard for the hazards of speculation in this area, there are grounds for suggesting that the Court is moving toward a more systematic approach to interpretation of those constitutional inhibitions on state taxation that, broadly speaking, bear on the allocation of powers between state and national governments in our federal system. The evidence for this hypothesis - several recent decisions handed down by the Court over a relatively brief period-is admittedly fragmentary, but it is sufficient to warrant a preliminary inquiry and some tentative conclusions.

The first section of this Article examines three recent cases, each addressed to a different constitutional limitation on the scope of state tax power, that may be read as signifying a new approach: Michelin Tire Corp. v. Wages, which concerned the import-export clause; United States v. County of Fresno, which concerned the supremacy clause; and Complete Auto Transit, Inc. v. Brady, which concerned the commerce clause. Section II considers the implications of these decisions and explores the possibility that they share an underlying doctrinal unity.