In legal writing, “shall” creates a binding duty and “should” offers a recommendation, so the choice between should and shall in law usually marks the line between an enforceable obligation and advice you’re free to weigh. That’s the default. Courts, however, have read “shall” in more than one way depending on context, and “should” can carry real weight when it appears in professional guidelines. Knowing where each word binds you and where it doesn’t is the point.
What “Shall” Means
When a contract or statute says a party “shall” do something, the ordinary reading is that the action is mandatory. Cornell Law’s Legal Information Institute notes that courts “ordinarily construe the word ‘may’ as permissive and the word ‘shall’ as mandatory, particularly when a single statute uses both terms.”1LII / Legal Information Institute – Law.Cornell.Edu. Shall That side-by-side usage is one of the clearest signals that the drafter meant “shall” to compel.
The consequences of ignoring a “shall” provision are concrete. In a contract, failing to perform an action labeled “shall” typically constitutes a breach and opens the door to damages, termination, or equitable remedies like specific performance. In a statute, ignoring a “shall” requirement can trigger penalties, invalidate a government action, or give an affected party grounds to challenge a decision in court.
So if your lease says “the tenant shall maintain renter’s insurance throughout the lease term,” you have a binding obligation. Skipping the insurance isn’t a judgment call; it’s a breach.
When “Shall” Isn’t Actually Mandatory
The complication is that “shall” doesn’t always carry the force it appears to. Courts distinguish between mandatory provisions, where a violation invalidates the action, and directory provisions, where the requirement guides conduct but a misstep doesn’t automatically void the proceeding.
Cornell Law explains that “shall” does not have “a fixed or inflexible meaning and may be given a permissive or directory interpretation depending on the legislative intent.” If a provision using “shall” merely directs how officials should conduct proceedings or maintain order, courts often treat it as directory rather than mandatory.1LII / Legal Information Institute – Law.Cornell.Edu. Shall A mandatory “shall” in a criminal sentencing statute strips the judge of discretion. A directory “shall” in a procedural rule about filing deadlines might mean a late filing is an irregularity that can be corrected, not a fatal defect.
One practical test courts have used: whether the affected party can waive the objection. If a party can agree to overlook the violation, the provision is likely directory. If no one can waive it, the provision is likely mandatory.
Drafters also create a problem known as the “false imperative,” where “shall” appears in a sentence that doesn’t actually impose a duty on anyone. The National Conference of State Legislatures describes this as “nonsense” because “the imperative appears to command when it does not.”2National Conference of State Legislatures. RELACS Report – The False Imperative A line like “Service shall be made on the parties” sounds mandatory but doesn’t name who has the duty.
In Gutierrez de Martinez v. Lamagno (1995), the U.S. Supreme Court confronted a statute saying the United States “shall” be substituted as a party defendant once the Attorney General certified an employee was acting within the scope of employment. The Court acknowledged the language was “far from clear” and held that “shall” in that context did not strip courts of review power. Writing for the majority, the Court observed that legal writers “sometimes use, or misuse, ‘shall’ to mean ‘should,’ ‘will,’ or even ‘may.'”3Justia Law. Gutierrez de Martinez v. Lamagno, 515 U.S. 417 (1995) When the Supreme Court itself reads “shall” as “may,” the word has a credibility problem.
What “Should” Means
“Should” recommends; it doesn’t require. A clause stating “the parties should attempt mediation before filing suit” encourages mediation. Skipping that step won’t constitute a breach.
Failing to follow a “should” provision generally doesn’t expose you to penalties, contract termination, or statutory liability. The Scribes Journal of Legal Writing notes that a directory provision, which carries roughly the meaning of “should,” does not invalidate proceedings unless the other side can show actual prejudice from the deviation.4Scribes. The Many Misuses of Shall That’s a high bar. “Should” gives you room to exercise judgment without automatic consequences for choosing a different path.
When “Should” Carries More Weight
In professional fields like medicine, engineering, and accounting, industry guidelines frequently use “should” to describe best practices. Those guidelines aren’t statutes, but in a negligence lawsuit they can become powerful evidence of what a reasonable professional would have done. If a medical association’s guidelines say a doctor “should” order a particular test given certain symptoms, and the doctor skips it, a plaintiff’s attorney will put that guideline in front of a jury to argue the doctor fell below the standard of care.
Guidelines are not identical to the standard of care. Following them doesn’t guarantee you were careful enough, and deviating from them doesn’t automatically make you negligent. But the gap between “advisory” and “irrelevant” is smaller than many professionals assume. If you deviate from a “should” recommendation in your field, documenting your reasoning is the best way to protect yourself later.
“Shall” vs. “May”
Reading “shall” accurately usually means reading it against “may.” While “shall” creates a duty, “may” grants discretion. A statute saying an agency “may” impose a fine gives that agency the choice of whether to act. A statute saying the agency “shall” impose a fine removes that choice.
Cornell Law defines “may” as “an expression of possibility, a permissive choice to act or not, and ordinarily implies some degree of discretion.” In contracts, “may” signals permission, liberty, or power rather than a mandatory requirement.5LII / Legal Information Institute – Law.Cornell.Edu. May “The landlord may terminate this lease upon thirty days’ notice” means the landlord has the option; it does not compel termination.
The contrast matters most when a single document uses both terms. Courts treat that parallel usage as strong evidence the drafter chose each word deliberately.5LII / Legal Information Institute – Law.Cornell.Edu. May If a regulation says an applicant “shall” submit three forms and the reviewing officer “may” request additional documentation, the three forms are required and the extra documentation is at the officer’s discretion.
The Shift from “Shall” to “Must”
Because of all the confusion “shall” creates, modern drafting has been moving away from it. The Federal Rules of Civil Procedure were overhauled in 2007 to replace “shall” with “must,” “should,” or “may” throughout. The stated goal was “to make them more easily understood and to make style and terminology consistent throughout the rules.”6Legal Information Institute (LII) / Cornell Law School. Rule 15 – Amended and Supplemental Pleadings
The Plain Writing Act of 2010 pushed federal agencies in the same direction, requiring “clear, concise, well-organized” language in documents they issue or substantially revise.7GovInfo. Public Law 111-274 – Plain Writing Act of 2010 The U.S. Office of Personnel Management’s plain language guidance puts it directly: “Use ‘must’ instead of ‘shall.'”8U.S. Office of Personnel Management. Plain Language Nobody argues about whether “must” is mandatory, directory, or permissive.
Reading and Drafting the Words Correctly
If you’re reviewing a contract, lease, or regulation, pay close attention to which obligations use “shall” (or “must”) versus “should” or “may.” The mandatory provisions are the ones that create legal exposure if ignored. The “should” provisions are best practices worth following but won’t create liability on their own, unless they overlap with a professional standard of care in your field.
When you’re reading older documents that still use “shall,” check whether the same document also uses “may” or “should” elsewhere. That parallel usage is your best clue that the drafter meant “shall” to be truly mandatory. If “shall” appears in every sentence regardless of context, the drafter may have been using it loosely, and a court might treat some of those provisions as directory. Context controls over any single word.
If you’re drafting, drop “shall” and use “must” for obligations, “may” for permissions, and “should” for recommendations. Every ambiguous “shall” is a potential dispute waiting for the right set of facts. Using “must” avoids that risk and costs nothing in legal force.