concurring in the judgment.
I agree with Justice O’Connor that Arkansas should not be held to have violated the Constitution in imposing its Arkansas Highway Use Equalization Tax (HUE) before our decision in American Trucking Assns., Inc. v. Scheiner, 483 *201U. S. 266 (1987), yet should be held to have violated the Constitution in imposing that tax after Scheiner was announced. My reasons, however, diverge from hers in a fundamental way, which requires some explanation.
I share Justice Stevens’ perception that prospective decisionmaking is incompatible with the judicial role, which is to say what the law is, not to prescribe what it shall be. The very framing of the issue that we purport to decide today—whether our decision in Scheiner shall “apply” retroactively—presupposes a view of our decisions as creating the law, as opposed to declaring what the law already is. Such a view is contrary to that understanding of “the judicial Power,” U. S. Const., Art. III, § 1, which is not only the common and traditional one, but which is the only one that can justify courts in denying force and effect to the unconstitutional enactments of duly elected legislatures, see Marbury v. Madison, 1 Cranch 137 (1803)—the very exercise of judicial power asserted in Scheiner. To hold a governmental Act to be unconstitutional is not to announce that we forbid it, but that the Constitution forbids it; and when, as in this case, the constitutionality of a state statute is placed in issue, the question is not whether some decision of ours “applies” in the way that a law applies; the question is whether the Constitution, as interpreted in that decision, invalidates the statute. Since the Constitution does not change from year to year; since it does not conform to our decisions, but our decisions are supposed to conform to it; the notion that our interpretation of the Constitution in a particular decision could take prospective form does not make sense. Either enforcement of the statute at issue in Scheiner (which occurred before our decision there) was unconstitutional, or it was not; if it was, then so is enforcement of all identical statutes in other States, whether occurring before or after our decision; and if it was not, then Scheiner was wrong, and the issue of whether to “apply” that decision needs no further attention.
*202I dissented in Scheiner, and in that case and elsewhere have registered my disagreement with the so-called “negative” Commerce Clause jurisprudence of which it is but one, typically destabilizing, instance. See Scheiner, supra, at 303-306 (Scalia, J., dissenting); Tyler Pipe Industries, Inc. v. Washington State Dept. of Revenue, 483 U. S. 232, 259-265 (1987) (Scalia, J., concurring in part and dissenting in part). This disagreement rests on more than my view (by no means mine alone) that that jurisprudence is a “‘quagmire,’” id., at 259, quoting Northwestern States Portland Cement Co. v. Minnesota, 358 U. S. 450, 458 (1959), that it has been “ ‘arbitrary, conclusory, and irreconcilable with the constitutional text,’” since its inception in the last century, 483 U. S., at 260, n. 3, quoting D. Currie, The Constitution in the Supreme Court: The First Hundred Years 1789-1888, p. 234 (1985), and that it has only worsened with age. I believe that this jurisprudence takes us, self-consciously and avowedly, beyond the judicial role itself. The text from which we take our authority to act in this field provides only that “Congress shall have Power . . . To regulate Commerce . . . among the several States,” U. S. Const., Art. I, § 8, cl. 3. It is nothing more than a grant of power to Congress, not the courts; and that grant to Congress cannot be read as being exclusive of the States, as even a casual comparison with other provisions of Article I will reveal. See Tyler Pipe Industries, supra, at 261. The Commerce Clause, therefore, may properly be thought to prohibit state regulation of commerce only indirectly—that is, to the extent that Congress’ exercise of its Commerce Clause powers pre-empts state legislation under the Supremacy Clause, Art. VI, cl. 2. When we prohibit a certain form of state regulation that does not conflict with any federal statute, we are saying, in effect, that we presume from Congress’ silence that, in the exercise of its commerce-regulating function, it means to prohibit state regulation. 483 U. S., at 262-263. There is no other way to explain how state legislation that would (according to *203our “negative” Commerce Clause jurisprudence) violate the Constitution can nonetheless be authorized by a federal statute if Congress “disagree[s]” with our appraisal of the appropriate role of the States in the relevant field. See Scheiner, supra, at 289, n. 23.
Presuming law from congressional silence is quite different from the normal judicial task of interpreting and applying text or determining and applying common-law tradition. The principal question to be asked, of course, is what would a reasonable federal regulator of commerce intend—which is no different from the question a legislator himself must ask. That explains, I think, why no body of our decisional law has changed as regularly as our “negative” Commerce Clause jurisprudence. Change is almost its natural state, as it is the natural state of legislation in a constantly changing national economy. That also explains why our exercise of the “negative” Commerce Clause function has ultimately cast us in the essentially legislative role of weighing the imponderable—balancing the importance of the State’s interest in this or that (an importance that different citizens would assess differently) against the degree of impairment of commerce. See, e. g., CTS Corp. v. Dynamics Corp. of America, 481 U. S. 69, 89-94 (1987); Edgar v. MITE Corp., 457 U. S. 624 (1982); Pike v. Bruce Church, Inc., 397 U. S. 137 (1970). The “negative” Commerce Clause is inherently unpredictable-unpredictable not just because we have applied its standards poorly or inconsistently, but because it requires us and the lower courts to accommodate, like a legislature, the inevitably shifting variables of a national economy. Whatever it is that we are expounding in this area, it is not a Constitution.
Because our “negative” Commerce Clause jurisprudence is inherently unstable, it will repeatedly result in the upsetting of settled expectations. My fellow dissenters in Scheiner seek to avoid this consequence in the present case—or, more precisely, seek to avoid extending this consequence beyond *204the unfortunate State before the Court in Scheiner, to all other States that had similar laws—by embracing a rule of prospective decisionmaking. There is some appeal to that approach in the “negative” Commerce Clause field: If we are making essentially legislative judgments, why not make them in legislative fashion, i. e., prospectively (subject, of course, to the limitation of the case-or-controversy requirement of Article III, § 2, cl. 1, which surely requires retro-activity with respect to the parties immediately before the Court)? I decline to adopt that solution because, as I have discussed above, such a mode of action is fundamentally beyond judicial power—and although “negative” Commerce Clause decisionmaking is as well, two wrongs do not make a right.
But it does not follow that I must conclude that the pre-Scheiner Arkansas HUE taxes were unconstitutional. Given my disagreement with this Court’s “negative” Commerce Clause jurisprudence, the only thing that could possibly lead me to such a conclusion would be Scheiner’s status as precedent. Although I will not apply “negative” Commerce Clause decisional theories to new matters coming before us, stare decisis—that is to say, a respect for the needs of stability in our legal system—would normally cause me to adhere to a decision of this Court already rendered as to the unconstitutionality of a particular type of state law. The law here is indistinguishable from that in Scheiner, so I would normally suppress my earlier view of the matter and acquiesce in the Court’s opinion that it is unconstitutional. Something is wrong, however, if I must take that position with respect to the pre-Scheiner taxes at issue in the present case. Believing that Arkansas was fully entitled to impose the taxes, I would nonetheless make the fifth vote to penalize it for having done so even during the period (pre-Scheiner) when our opinions announced it could lawfully do so—and I would impose this injustice in the name of stare decisis, that is, in the interest of protecting settled expectations. That would be *205absurd. Though I do not believe I have the option of suspending the principle of retroactive judicial decisionmaking, the doctrine of stare decisis is a flexible command. I do not think that a sensible understanding of it requires me to vote contrary to my view of the law where such a vote would not only impose upon a litigant liability I think to be wrong, but would also upset that litigant’s settled expectations because the earlier decision for which stare decisis effect is claimed (Scheiner) overruled prior law. That would turn the doctrine of stare decisis against the very purpose for which it exists. I think it appropriate, in other words—indeed, I think it necessary—for a judge whose view of the law causes him to dissent from an overruling to persist in that position (at least where his vote is necessary to the disposition of the case) with respect to action taken before the overruling occurred.
Accordingly, I would affirm the decision below with respect to Arkansas’ HUE taxes imposed pre-Scheiner, because in my view they were constitutional. I would reverse the decision below with respect to Arkansas’ HUE taxes imposed post-Scheiner because they were unlawful by virtue of that decision. I thus concur in the judgment of the Court.