In a legal document, “shall” traditionally means the actor has a duty to do something and “may” means the actor has discretion to do it or not. That is the starting point for reading “shall” versus “may” in legal documents, but it is only a starting point: courts across the United States have repeatedly found that “shall” can mean “must,” “may,” “should,” “will,” or even “is entitled to,” depending on how the drafter used it. “May,” by contrast, is treated as reliably permissive. The practical effect is that a reader can usually take “may” at face value, while “shall” needs to be checked against the rest of the document.
The Default Rule
The mandatory/permissive canon of interpretation holds that mandatory words impose a duty and permissive words grant discretion. Antonin Scalia and Bryan Garner summarized it as “mandatory words impose a duty; permissive words grant discretion,” identifying “may” as the correct term for granting discretion.1Michigan Bar. May for Granting Discretion Richard Wydick’s Plain English for Lawyers lays out the full set of legal modal verbs: “must” means required to, “may” means has discretion to or is permitted to, “should” means ought to, and “will” expresses either a future contingency or a contractual obligation.2Illinois State Bar Association. Must vs. Shall
The U.S. Supreme Court has said repeatedly that “may” connotes discretion, and that this reading is especially clear when a statute uses “may” alongside “shall.” In Biden v. Texas (2022), the immigration provision at issue used “shall be detained” in one subsection and “may return” in another. The Court held that the choice of “may” granted authority rather than imposed a duty, and refused to read a mandatory obligation into language Congress deliberately made permissive.3Cornell Law Institute. Biden v. Texas As the Court put it: “The statute says ‘may.’ If Congress had intended [the provision] to operate as a mandatory cure … it would not have conveyed that intention through an unspoken inference in conflict with the unambiguous, express term ‘may.'”4Supreme Court of the United States. Biden v. Texas, 597 U.S. ___
Why “Shall” Is Not Reliable
Black’s Law Dictionary gives five definitions for “shall”: has a duty to; should; may (often when preceded by “not” or “no”); will (future tense); and is entitled to. Judge Frank Easterbrook of the Seventh Circuit called “shall” “a notoriously slippery word that careful drafters avoid.”5vLex. What Shall and Will
The Supreme Court conceded the problem in Gutierrez de Martinez v. Lamagno, 515 U.S. 417 (1995). Justice Ginsburg wrote that while “shall” generally means “must,” legal writers “sometimes use, or misuse, ‘shall’ to mean ‘should,’ ‘will,’ or even ‘may,'” and that courts “in virtually every English-speaking jurisdiction have held — by necessity — that shall may mean may in some contexts, and vice versa.”6Cornell Law Institute. Gutierrez de Martinez v. Lamagno, 515 U.S. 417 The Court held that the Westfall Act’s use of “shall” did not preclude judicial review of the Attorney General’s certification, rejecting the argument that the word mandated automatic, unreviewable substitution of the United States as defendant.7Justia. Gutierrez de Martinez v. Lamagno, 515 U.S. 417 More than 120 pages of the legal reference Words and Phrases are devoted to interpreting “shall.”8Michigan Bar. Shall and Will in Contracts Courts have read the word as “must” (West Wisconsin Railway v. Foley, 94 U.S. 100), as “may” (Railroad Co. v. Hetch, 95 U.S. 168; Scott v. United States, 436 U.S. 128), and as something closer to a prediction than a command.9Holland & Knight. Canceling the Word Shall in Leases, Contracts, and Legal Forms
What Rides on the Reading
The ambiguity has real stakes. A provision read as “directory” means noncompliance is an irregularity that does not void the action; a provision read as “mandatory” means noncompliance invalidates it. A contract clause interpreted as a condition precedent rather than a promise can forfeit rights entirely. In one reported example, a farmer who destroyed tobacco stalks in violation of a clause using “shall” lost his insurance claim because the court read the clause as a condition the farmer had failed to meet.10Scribes. The Many Uses of Shall
Contract litigation turns on the same ambiguity. In Novozymes A/S v. Codexis, Inc., the Delaware Chancery Court confronted a technology licensing agreement in which each side flipped its reading of “shall” depending on which interpretation helped its position. Codexis argued that “shall” in one clause made license conversion automatic and mandatory; Novozymes argued that if “shall” was mandatory elsewhere, it also triggered a cure period for breach. The court denied summary judgment, found a genuine dispute about what the word meant, and described the case as a cautionary lesson in the importance of consistent drafting.5vLex. What Shall and Will
How Courts Decide Whether “Shall” Is Mandatory
When a statute tells an official to do something by a deadline and the official misses it, courts in many jurisdictions start from a presumption that procedural commands to government officials using “shall” are directory rather than mandatory.
The Illinois Supreme Court has worked this out in a series of cases. In In re M.I. (2013), the court ruled that a statutory deadline for a juvenile hearing was directory because the statute specified no consequence for missing the deadline and the respondent suffered no prejudice. Similar results followed in In re James W. (2014) and In re Rita P. (2014). Under Illinois law, a “shall” provision becomes mandatory only if the statute includes specific negative language prohibiting further action on noncompliance, or if a directory reading would injure the very right the provision was designed to protect.11Illinois State Bar Association. When the Term Shall Is Directory
Other common-law jurisdictions apply a similar analysis. The Irish framework from State (Elm Developments Ltd) v. An Bord Pleanála (1981) asks whether a requirement is “an integral and indispensable part of the statutory intendment”; if so, it is mandatory, and if not, substantial compliance may suffice. The factors courts weigh include the strength of the statutory language, how central the provision is to the statute’s purpose, the impact on individual rights, and whether the party actually suffered prejudice from the noncompliance.12Administrative Law Matters. Distinguishing Mandatory and Directory Provisions
Context governs more generally too. A Congressional Research Service report on statutory interpretation describes language canons, including the mandatory/permissive canon, as “axioms of experience” and “neutral, analytical guides,” not absolute rules. Because “statutory construction is a holistic endeavor,” the meaning of “shall” or “may” in any given provision is shaped by the statute’s structure, its definitions section, and its relationship to other provisions.13Every CRS Report. Statutory Interpretation: General Principles and Recent Trends The Michigan Court of Appeals has reinforced that “may” is permissive and will be read as mandatory only where legislative intent or structural inferences clearly require it.1Michigan Bar. May for Granting Discretion
The Shift From “Shall” to “Must”
Recognition that “shall” is unreliable has driven a broad move toward “must” in American legal drafting. The most visible example is the restyling of the Federal Rules of Civil Procedure, effective December 1, 2007. The Advisory Committee on Civil Rules, with drafting consultant Joseph Kimble, replaced every instance of “shall” with “must,” “may,” or “should,” depending on which term accurately captured the established interpretation of the rule.14Cornell Law Institute. Federal Rules of Civil Procedure, Rule 1 Kimble described “shall” as “notorious for its misuse and slipperiness in legal documents.”15Michigan Bar. Guiding Principles for Restyling the Civil Rules, Part 2 The committee’s notes explained that “shall” is “no longer generally used in spoken or clearly written English” and is “inherently ambiguous” because it can mean “must,” “may,” or something else depending on context.16Office of the Law Revision Counsel. Federal Rules of Civil Procedure, Committee Notes
The Plain Writing Act of 2010 extended the shift across federal agencies. Federal plain language guidelines state that “must is the clearest way to convey to your audience that they have to do something,” and agencies including the Office of the Federal Register and the Federal Aviation Administration have adopted handbooks requiring “must” in place of “shall.”9Holland & Knight. Canceling the Word Shall in Leases, Contracts, and Legal Forms At the state level, Utah’s legislative drafting manual directs drafters to use “shall” only for a true command, not to declare a legal result, and warns against “false imperatives.”17Utah Legislature. Utah Drafting Manual Canadian federal drafting standards now require “must” for obligations and “must not” for prohibitions in all new legislation, with “shall” permitted only in amendments to older statutes; British Columbia, Alberta, and Manitoba have amended their Interpretation Acts to confirm that “must” is imperative.18Department of Justice Canada. Legistics – Must and Shall Australia’s Commonwealth Office of Parliamentary Counsel formally replaced “shall” with “must” for obligations, following a 1987 recommendation from the Law Reform Commission of Victoria.19Melbourne Law School. Mandatory and Directory Rules in Australian Legislation
Reading “Shall” in a Contract
In private contract drafting, two leading voices disagree sharply about what to do. Bryan Garner argues that “shall” should be eliminated. He calls the traditional distinction between “shall” and “will” a “superstition” with “neither a basis in historical grammar nor the sound sanction of universal usage,” and describes “shall” as “peripheral in American English” with a usage that is “declining because of increased recognition of its hopeless ambiguity as actually misused by lawyers.”20LawProse. Garner’s Usage Tip of the Day: Shall and Will In non-consumer contracts, he recommends “will” for obligations; in consumer contracts, “must.”8Michigan Bar. Shall and Will in Contracts
Kenneth Adams, author of A Manual of Style for Contract Drafting, defends what he calls the “disciplined use” of “shall,” arguing that it is the only term that correctly imposes a duty on the subject of a sentence, meaning “has a duty to.” Adams considers “must” too “bossy in tone” for consistent use throughout a contract and objects that using “will” for both obligations and future statements conflates two different meanings. He disputes the claim that “shall” generates significant contract litigation, noting that most of the cases collected in Words and Phrases involve statutes, and he argues that replacing “shall” with “must” or “will” would not resolve the underlying question of whether a provision creates an obligation or a condition.21Adams on Contract Drafting. Shall His framework uses “shall” for duties of contracting parties, “must” for obligations imposed on third parties, and “will” for consequences contingent on future events.5vLex. What Shall and Will
The practical consensus, despite that disagreement, is that whichever term a drafter picks, it should be used consistently throughout the document and ideally defined within the contract itself.8Michigan Bar. Shall and Will in Contracts For a reader rather than a drafter, the sequence is the same: check whether the contract defines “shall,” look at how the word is used in neighboring clauses, and only then apply the default that “shall” is mandatory and “may” is permissive.
Where “Shall” Still Dominates
One boundary is worth flagging. While domestic systems have been steadily moving away from “shall,” the word remains the standard term for imposing legal obligations in treaties and international agreements. In instruments like the United Nations Charter (1945) and the European Convention on Human Rights (1950), “shall” is ubiquitous.22Lancaster University. The Role of Shall and Should in Two International Treaties Article 102 of the UN Charter, for example, provides that every treaty entered into by a member state “shall be registered with and published by the Secretariat.”23United Nations. Treaty Handbook The ECHR also uses “shall” extensively for prohibitions, often in the form “No one shall be” followed by a past participle. A reader working with treaty text should not expect the same shift to “must” that has occurred in domestic drafting.
So the short answer, applied to a document in hand: “may” almost always means discretion. “Shall” usually means a duty, but check the document’s definitions, read the surrounding provisions, and ask whether the drafter used “shall” consistently or mixed it with “must” and “will.” If the document is a federal rule, a modern state statute, or a federal agency regulation written after the plain-writing shift, you can expect “must” where older drafting would have said “shall,” with the same mandatory force.