Enumerating power by subject is a familiar feature of federal constitutions that aspire to apportion power among governments. Long-serving federal constitutions seem to say a lot more about how power to govern their communities should be distributed among their governments than about how those governments should treat each other. Yet those texts come no closer to supplying actual answers to disputes about power distribution than they do to disputes about institutional independence. Power enumeration is indeterminate not merely because subjects of power are abstract, but because federal constitutions are silent about aboutness. Federal drafting conventions that resorted to the judiciary to enforce power enumeration seemed to assume that the range of rationally conceivable ways to decide whether laws are inside or outside specified subjects of power (the range of rationally conceivable tests of aboutness) would generally yield the same answers. The assumption is false; laws do not have single subjects. Laws are almost always susceptible of more than one characterization, almost always about more than one thing. Power enumeration defaults to constitutional dispute resolvers an open discretion to decide what to make of it, and an adjudicative necessity to develop a law of aboutness. In deciding disputes about power distribution, as surely as in deciding disputes about intergovernmental independence, constitutional courts have unavoidably responded to constitutional silence with court-created core constitutional law. That law of characterization has sometimes deferred to rational legislative judgment, and sometimes not.Power enumeration was pioneered at the United States Constitution’s Philadelphia drafting convention against the wishes of key nationalist proponents of the Virginia Plan. Power enumeration was an initiative of localist delegates, who relied on a precedent that proved a poor fit for the compromise system that in fact emerged. Their precedent was the specification of subjects in treaties, and in particular the subject specification in the then-operative Articles of Confederation. Power distribution under the Articles was policed by the member states themselves, through their direct control of Congress. Under the localists’ New Jersey Plan, that would have stayed true, and required no judicial enforcement. The Connecticut Compromise maintained this localist vision by constituting the Senate as a true states’ house that resembled the existing Confederation Congress. Even after losing the final vote on the compromise, nationalist delegates bitterly opposed this outcome, until they realized that through a subtle and carefully-timed amendment they could make equal state representation in the Senate about the vocational interests of small-state political leaders rather than about preserving a federal balance. That change, which has received little analysis in the leading historical scholarship, turned the Senate back into the independent, elite institution that nationalists had wanted all along and stopped the Senate from becoming a reliable political safeguard of federalism. Immediately thereafter, the convention referred the task of enumerating Congress’s powers to a committee of detail. Edmund Randolph’s preliminary draft of the committee’s enumeration explicitly linked power enumeration to an arbitral role for the Supreme Court. Having adopted the New Jersey Plan’s vision of enumerated national powers but discarded that plan’s vision of a reliable political mechanism to keep Congress within those powers, the convention backed into depending on the courts to make power enumeration meaningful. Late in the convention’s life, delegates coalesced around explicitly committing to the Supreme Court jurisdiction to decide all cases arising under the Constitution.Power enumeration affords constitutional courts adjudicative discretion that may be exercised to promote not only a federal balance, but individual rights too. Courts could read down constitutional delegations to legislatures so as not to reach valued liberties and not to permit invidious distinctions, much as some common law courts read down statutory delegations to executives. In this way, courts could vindicate the Founding-era Federalist claim that, for example, a law about interstate commerce cannot also be about freedom of speech. A constitutional court could construct a whole implied bill of rights to limit a government of enumerated powers.