This week, Noah H. Marks (UNC) reviews a new article by Sarah B. Lawsky (Illinois), Limiting Inconsistencies in Legal Languages, 28 Vanderbilt J. Ent. & Tech. L. 765 (2026).

Tax practitioners, professors, and students are all too aware that the Code, despite its interconnectedness and intricacies, is far from a logically consistent, unified whole. Overlapping provisions and statutory gaps reflect the Code’s human authorship, and IRS guidance and glosses from Treasury Regulations, informal guidance, and Forms and Instructions resolve some of those issues, while exacerbating (and even introducing) others.

Sarah Lawsky’s recent piece, Limiting Inconsistencies in Legal Languages, grapples with the implications of translating contradictory Code provisions into the logical binaries and fixed rules that define computer code. Building on her other articles that demonstrate how formal logic and programming languages should be tools to help understand and improve tax law, this article focuses on inconsistencies and offers a promising way to leverage code to identify inconsistencies within the Code.

The article begins by contrasting inconsistencies in standard classical logic with inconsistencies in statutory texts. In standard logic, accepting contradictory propositions is referred to as the “principle of explosion” because it results in being able to logically prove any proposition whatsoever. Lawsky does an excellent job laying out just why contradictory truths blow up traditional logic, even for readers (like me) who have never (or only rarely, or only long ago) studied formal logic in mathematics or philosophy.

In law, by contrast, the article highlights that various accepted conventions resolve seemingly facial, irresolvable statutory inconsistencies. Prioritization is one example: the rule that the specific governs the general; the rule that a later in time statute is read as amending an earlier in time provision; the rule that exceptions trump general provisions. Another example of prioritization turns on the source of law (e.g., federal versus state). More subtly, statutory provisions can also be read as setting floors or ceilings, rather than mandating their express outcomes. For example, in tax, a provision saying that you must remit $10 and another saying that you must remit $20 are harmonized by reading the former as a floor (remit at least $10, rather than exactly $10) and recognizing that complying with the latter necessarily includes complying with the former (as so read). On top of these rules, tax law adds its own substantive canons of construction that have waxed and waned, such as strictly construing tax exemptions against taxpayers. And if (when) these statutory-text focused approaches are insufficient, administrative guidance and judicial glosses exist to clarify one’s legal obligations.

To concretize these abstract points, the article turns to a lengthy, interesting dissection of Section 121, which appears to include contradictory rules regarding the exclusion of certain gain from the sale of a principal residence for married taxpayers who file jointly. In short, it is not clear how Section 121(b)(2)(B) interacts with Section 121(c). Here’s a brief refresher on Section 121’s mechanics:

• Sections 121(a) & (b)(1) allow a taxpayer to exclude up to $250,000 in gross income from a sale of the taxpayer’s principal residence if the taxpayer meets certain ownership duration, use duration, and sale infrequency requirements.
• Section 121(b)(2)(A) specifies that married persons filing a joint return can exclude up to $500,000 in gross income (instead of $250,000) if they meet certain modified statutory requirements.
  • Section 121(b)(2)(B), in turn, says that if married persons filing a joint return do not meet Section 121(b)(2)(A)’s requirements, their exclusion is, instead, up to “the sum” of the amounts “to which each spouse would be entitled if such spouses had not been married.”
    • For the purposes of this hypothetical application of Section 121(a) & (b)(1), each spouse is treated as owning the property during the period in which either spouse owned the property.
• Section 121(c) prorates the “applicable” “dollar limitation” in Section 121(b)(1) or (2) for a taxpayer who does not meet the aforementioned requirements but who is selling for certain specified reasons.

The article unpacks how, on the face of the statute, it is not clear whether Section 121(c)’s “applicable” “dollar limitation” for taxpayers subject to Section 121(b)(2)(B) is each taxpayer’s hypothetical individual amount, prorated separately, or if it is the $500,000 specified in Section 121(b)(2)(A), prorated together. Notably, the legal conventions discussed above do not resolve this: Section 121 was enacted all at once by Congress, it is at a single level of specificity, and it is a single exclusion regime. Treasury and the IRS, however, have resolved this question in publications and worksheets (in favor of the separate, sum of limitations approach). Usually, this is a taxpayer-favorable outcome, meaning that standing requirements limit the ability to challenge this administrative choice.

With this known inconsistency in hand, the article then applies programming tools to highlight the challenges raised in bridging these domains. The article first discusses encoding Section 121’s rules into the Z3 theorem prover program. To successfully do so, however, the coder must make reasonable judgments about how to encode the intersection of Section 121(b)(2)(B) and Section 121(c). In this particular instance, the path of least resistance is to follow Treasury and the IRS’s forms and instructions (which is, presumably, what TurboTax and other tax preparation software do), but that’s only available because a legal actor has addressed the question.

The article’s primary argument addresses the rest of the time, where the Code is inconsistent, legal tools for resolving the inconsistency are insufficient, and there isn’t any additional guidance or gloss. Because computer code aligns with standard classical logic and must, therefore, tie out, either the inconsistent provisions cannot be coded (which is often untenable) or the coder must make assumptions and choices. But the coder is (usually) not a legal actor and, Lawsky argues, legal actors are the ones who should be resolving legal inconsistencies, not coders. Accordingly, the appropriate role of code is to flag and highlight the inconsistency. The balance of the article demonstrates how the domain specific programming language Catala can be used to do just that—and, ultimately, make the branching alternatives explicit.

Legislative drafters (inside and outside of government) interested in improving the Code’s coherence should follow Lawsky’s suggestion of using Catala on the front end of the legislative process. Of course, that is easier to do when the in-formulation legislation is a unified whole. For legislation making more surgical revisions to the Code (e.g., revising Section 121 to eliminate the ambiguity flagged above), presumably you’d need to layer the Catala code for such revisions into a broader Catala code base reflecting existing Section 121 (and this complexity would scale as surgical revisions impact more Code provisions). In addition, it seems to me that the Catala code would be a very helpful tool on the back end too. Stakeholders could use it to advise Treasury and the IRS about guidance areas to prioritize, to prepare comments on proposed regulations, and to highlight inconsistencies and gaps in forms and instructions. And, on the flip side, the government could use it to draft better guidance. Ultimately, we’d all be well advised to leverage and build on this article’s Catala code foundation to improve the Code’s—and tax law’s—consistency and coherence.

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

Zeba Ahmed (Hamdard Institute), Input Tax Credit and Supplier Compliance Under GST: A Critical Legal Analysis (May 15, 2026)

Rifat Azam (Reichman University), Public International Law and Tax Law: Taxpayers’ Rights: The International Law Association’s Project on International Tax Law (May 11, 2021)

Leonie Babilas (Humboldt) & Karina Körösi (Humboldt), How Much and From Whom? An Information Experiment on Tax Misperceptions and Redistribution Preferences, TRR 266 Accounting for Transparency Working Paper Series No. 240 (May 27, 2026)

Anthony Deininger (Oklahoma), Taxation by Inertia: Conditional Design and the Withdrawal of Section 280E Enforcement Authority (April 20, 2026)

Daria Demidenko (Moscow State Institute of International Relations), Socially Equitable Taxation of Individuals’ Income and Real Estate: The Case of the People’s Republic of China (March 1, 2026)

Daria Demidenko (Moscow State Institute of International Relations), The Concept of “Technical Services” for Tax Purposes in International Transactions (March 9, 2026)

Alejandro Díaz Siva (Independent), The Constitutional and Economic Case Against Recurrent Property Taxation on Primary Residences: A Critical Analysis of Chile’s Impuesto Territorial in Comparative Perspective (May 3, 2026)

Lorraine Eden (Texas A&M), Efficiency and Market Power: The Two Faces of the Multinational Enterprise (May 25, 2026)

Can Eken (Durham University), Costs and Funding Investment Arbitration Cases: What Are the Problems? What Are the Solutions?, 59 Int’l Law 89 (2026)

Dhruv Janssen-Sanghavi (Maastricht), 2026 Amendments to GAAR: Tiger Global and the Limits of Grandfathering (April 16, 2026)

Dalié Jiménez (Irvine), Jonathan Glater (UCLA), Andrew Martin (Merced) & Charlie Eaton (Merced), Public Power, Private Debts: The Misuse of California’s Tax Intercept Power for Private Colleges, Yale L.J. Forum (forthcoming 2026)

Tolkin Kholbazarov (University of World Economy and Diplomacy), Cryptocurrency Regulation in the Republic of Uzbekistan: Legal Status of Service Providers and the Question of Cross-border Acquisitions by Crypto-Magazines (May 16, 2026)

Mary Leto Pareja (New Mexico), Deathbed Dilemmas: A Proposal to Advance the Step Up in Basis to Address Tax Burdens on the Terminally Ill (May 1, 2026)

Ralf Maiterth (Humbolt), Yuri Piper (Paderborn) & Cornelius Schneider (Mannheim), Preferences for Taxing Wealth and Income, TRR 266 Accounting for Transparency Working Paper Series No. 239 (May 26, 2026)

Rajagopal Perumal, Taxing Value Without Presence (May 6, 2026)

Mansi S. Rai (Rochester), From Jurisdiction to Administrative Capability: Reconstructing State Tax Enforcement in the Digital Economy (April 30, 2026)

Mansi S. Rai (Rochester), Parallel Civilization Evolution—A Comparative Framework for Understanding the Axial Transformation (c. 500 BCE) (April 15, 2026)

Gaston Rey (Independent), Causal Imputation of Automation in Labor Law: Why AI Is Not Force Majeure—The Hangzhou Ruling (Zhou v. Tech Co., 2026) (May 6, 2026)

Tiago Alves Voss dos Reis (Fundação Getulio Vargas Law School), Interpretative Limits of the Tax Resources Administration Council from the Treasury Department (February 1, 2012)