William J. Brennan, Jr.

“ But far more common in our complex economy is the kind of sale presented in this case, which exhibits significant contacts with more than one State. In such a situation, it is the commercial activity within the State, and not the sales volume, which determines the State's power to tax, and by which the tax must be apportioned. While the ratio of in-state to out-of-state sales is often taken into account as one factor among others in apportioning a firm's total net income, see, e.g., the description of the 'Massachusetts Formula' in Note, 75 Harv.L.Rev. ”