This week, Jeff Gordon (Vanderbilt, Google Scholar) reviews Conor Clarke (Wash. U., Google Scholar) & Ari Glogower (Northwestern, Google Scholar), The Indirect Taxes, 102 Notre Dame L. Rev. __ (forthcoming 2027).

From the founding era to Moore, most of the major constitutional tax law cases revolve around the question of how to define a “direct tax,” that slippery concept that the Constitution says must be “apportioned” among the states. After contributing plenty to that question in prior work, Conor Clarke and Ari Glogower now turn to the inverse formulation: what exactly are the duties, imposts, and excises that the Constitution names as apparent alternatives—in other words, what are indirect taxes?

Neither the Constitution itself nor founding-era commentary is a very helpful guide on this question. From the text of Article I, Sections 8 and 9, it is not clear whether “taxes” and “direct taxes” are the same concept; whether taxes, duties, imposts, and excises are four distinct terms or are interchangeable; and whether the “direct” and “indirect” categories each have an affirmative meaning, or whether one is a residual category for whatever taxes don’t fit in the other, or whether the two categories are not even collectively exhaustive. Founding-era materials evince ambiguity, differences of opinion, and a general lack of linguistic precision about these potentially distinct concepts.

And so, Clarke and Glogower look to legislative practice. They examine the full sweep of federal statutes imposing unapportioned taxes between 1789 and 1913 (the year of the Sixteenth Amendment). Insofar as these statutes did not face or survived constitutional challenges, we can conclude that they represented “indirect” taxes. This attention to practice as a method of constitutional interpretation, known as “liquidation,” has gained a measure of academic popularity and was endorsed by Justice Kavanaugh in Moore.

What the authors find in the long nineteenth century is that Congress was perpetually flexible. It was flexible in its terminology, using the term “duty” broadly and arguably coextensively with “tax.” It was flexible in the tax bases it targeted, often refining a tax on a particular industry to move from taxing output, to taxing property and machinery, to taxing revenues, to eventually taxing something we would recognize as income. And it was even flexible on the distinction between direct and indirect taxes: an 1815 tax on watches and household furniture was not apportioned and was not challenged, even though it was a tax on property (which commentators have generally assumed makes a tax “direct”). The authors read this history as a gradual, continuous march toward an income tax. As early as 1814, a tax on the profession of banking was principally based on transaction volume, but bankers could elect to instead pay 1.5% of annual profits. Other profession-specific taxes accumulated, such that the eventual arrival of the income tax can be viewed as consolidating a hodgepodge of income-like components rather than breaking with all that came before it.

For Clarke and Glogower, the main lesson of this history is to eschew formalism in constitutional tax analysis. The universe of permissible indirect taxes seemed to expand over time as the practical possibilities for Congress’s tax base did. Throughout a period of great change in taxation, the categories of “impost,” “duty,” and “excise” did not constrain Congress in developing its tax power; if anything, the terms stretched to fit the practice. While this narrative is persuasive in its own right, it leaves some uncertainty about what meaning of “direct tax” is left over at the end. Of course, the authors have elsewhere provided sophisticated accounts of how the direct tax rule should interact with wealth taxes and other taxes on property. But it would be useful to clarify whether the historical material in this Article provides any principles for line-drawing, or whether (as is the tempting conclusion) the distinction is completely indeterminate.

The Article will probably be read mainly for its constitutional law lessons, but it is equally valuable as a lesson in the practical challenges that explain the evolution of tax administration. The historical actors that Clarke and Glogower introduce were generally less concerned about constitutionality than about administrability. Commentators on the 1894 income tax (the one struck down in Pollock) did not view it as conceptually novel, just broader in its coverage than the sector-specific taxes that had come before. For better or worse, Congress rarely let conceptual elegance get in the way of the taxing power. It taxed the economic stocks and flows that it was able to measure at any given time. It regularly imposed taxes on bases that were rough proxies for a given industry’s ability to pay, before shifting the base to a better proxy a few years later. We face similar tradeoffs with imperfect proxies today, from proposed data center taxes as a proxy for the AI industry, to credits for increasing research expenditures as a proxy for innovation effort. The nineteenth century history provides some reassurance against perfectionism on these fronts.

Here is the rest of this week’s SSRN Tax Roundup:

Fadindra Prasad Acharya (Inland Rev. Dept., Nepal), Restructuring International Service Taxation: Why Is the New Article 12AA a Gamechanger for Developing Countries? (Sept. 8, 2026)

Zeba Ahmed (Hamdard Inst. Legal Stud. & Rsch.), Input Tax Credit Reversal Under Section 16(2)(c) of the CGST Act: Reconciling Revenue Protection with Taxpayer Rights and Constitutional Fairness (Sept. 11, 2026)

Maarten Floris de Wilde (Erasmus U. Rotterdam), From Multilateralism to Strategic Realism: A Proposal for a Corporate Tax 2.0 (July 1, 2026)

Brian D. Galle (UC Berkeley), David Gamage (Missouri) & Darien Shanske (UC Davis), Analysis of the Impacts of Propositions 41 and 42 on California Public Finance (Sept. 9, 2026)

Hans Gribnau (Tilburg L. Sch.), Jane Frecknall-Hughes (U. Nottingham) & Onno Ydema (Leiden U.), Examining the Influences on English Excise Taxes, After 1643, in 12 Studies in the History of Tax Law 55 (Dominic de Cogan & Peter Harris eds., 2025)

Hans Gribnau (Tilburg L. Sch.), Tax Advisers as Gatekeepers (Nov. 12, 2025)

Emer Hunt (Sutherland Sch. L., U. Coll. Dublin), The Tax Relationship Between Ireland and Apple: Under the State Aid Microscope, 147 CJEU—Recent Developments in Direct Taxation 2024 (Alexander Rust et al. eds., 2025)

Jeffery M. Kadet (Washington) & Reuven S. Avi-Yonah (Michigan), Periodic Adjustments—The Dialogue Continues, 192 Tax Notes Fed. 1457 Aug. 24, 2026)

Andres Knobel (Tax Justice Network), Integrating the Collection, Use and Exchange of Real Estate Ownership Information (July 1, 2026)

Hanok Lanke (Independent), Which Tax Incentives Survive Pillar Two? A Comparative Simulation of QDMTT Exposure Across Six Incentive Archetypes (Sept. 9, 2026)

Ava Liu (Harvard), Technology Governance in the Age of AI: From Redistribution to Predistribution (Sept. 12, 2026)

Michael Motala (Tulsa), Global Corporate Tax Governance: Crisis, Consensus, Revolution (June 4, 2026)

Michael Motala (Tulsa), Tax Sovereignty and Investor Protection: Why the Proposed Global Minimum Tax Is Not the Final Frontier for Corporate Tax Arbitrage (June 3, 2026)

João Félix Pinto Nogueira (Int’l Bureau of Fiscal Documentation), Tax Administration and Technology: From Enhanced to No-Cooperation? (June 2, 2026)

Orli Oren-Kolbinger (Oregon), Do Tax Judges Favor the Tax Authority?, 28 Fla. Tax Rev. 91 2024)

Orli Oren-Kolbinger (Oregon), Judging Women: Benevolent Sexism and Innocent Spouse Relief in the United States Tax Court, 28 U. Pa. J. Bus. L. 49 (2025)

Orli Oren-Kolbinger (Oregon), Timing Matters: Sequencing AI in Tax Education, 24 Pitt. Tax Rev. __ (forthcoming 2026)

Alex Raskolnikov (Columbia), Taxation and Formal Equality, 107 Wash. U. L. Rev. __ (forthcoming 2027)

Amedeo Rizzo (Oxford), E-Compliance and Emerging Technologies in Tax Law: A Comparative Legal Inquiry Between the E.U. and the U.S., Stanford-Vienna TTLF Working Paper No. 157 (2026)

Dallas Salisbury (Employee Benefit Rsch. Inst.), ERISA at 52: Where Is the Employer-Sponsored System Going, and Who Is It Leaving Behind? (Jan. 8, 2026)

Siddhi Widyaprathama (Juwono Widyaprathama & Rekan), The Attribution Problem (Sept. 11, 2026)