Definition
In law, the days of the week are the seven named calendar days — Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday — treated as legally significant units for purposes of computing time, determining the validity of legal acts, establishing deadlines, and identifying court holidays and non-judicial days. Courts take judicial notice of the days of the week without requiring proof, meaning that a court will independently verify which day of the week corresponds to any given calendar date when that fact becomes legally relevant. The practical consequence is that a legal act performed on a day prohibited by law — such as executing process on a Sunday — may be rendered void or voidable regardless of whether the parties were aware of the problem.
Common Confusion
The phrase "days of the week" is occasionally conflated with related time-computation concepts that carry distinct legal meanings. "Calendar days" counts every day including weekends and holidays. "Court days" or "judicial days" counts only days the court is open. "Business days" typically excludes weekends and public holidays. When a statute or rule specifies a deadline in "days" without qualification, the default rule varies by jurisdiction and by the applicable procedural code — it does not automatically mean calendar days, court days, or business days. Researchers working with historical materials must be especially careful: older statutes and rules often omitted the qualifier entirely, leaving the applicable meaning to be resolved by case law.
Why It Matters in Research
The legal significance of days of the week generates research traps at several levels.
First, Sunday occupies a historically distinct legal category. At common law and under many early American statutes, Sunday was a dies non juridicus — a non-judicial day on which legal process could not be served, courts could not sit, and certain contracts could not be formed. This rule was not merely ceremonial. As Bouvier's entry illustrates, a writ of inquiry executed on a Sunday was held defective. Researchers working with pre-twentieth-century materials should assume that Sunday prohibitions were in effect unless affirmatively displaced by statute, and should check whether a given jurisdiction's Sunday laws were civil, criminal, or both.
Second, the judicial notice rule cuts both ways in historical sources. Because courts always take judicial notice of what day of the week a date falls on, litigants and their counsel rarely bothered to plead or prove the day explicitly. This means that a defect based on a Sunday execution or a prohibited day may appear in the record only as a technical objection buried in pleadings or a brief notation in the court's ruling — not as a prominently labeled "Sunday law" issue. Keyword searches for "Sunday" alone will miss cases where the day was identified only by date.
Third, deadline computation is a persistent source of modern research confusion. Federal and state procedural rules have been repeatedly amended to clarify whether deadlines expressed in days include or exclude weekends and holidays, and whether the last day of a period that falls on a Sunday or holiday is extended to the next business day. The current version of Federal Rule of Civil Procedure 6 embodies this logic explicitly, but its predecessors were less clear. When researching whether a filing was timely in a historical case, the researcher must apply the version of the rule in effect at the time — not the current version.
Fourth, filing deadlines keyed to specific day-counts appear throughout the Law Mind corpus in specialized contexts. The 90-day deadline for petitioning the Tax Court following an IRS Notice of Deficiency and the 30-day deadline for filing a petition for review of an immigration decision are both day-counted periods where the day-of-the-week on which the period expires is legally consequential. In both contexts, a period ending on a Sunday or federal holiday is governed by extension rules that must be verified against the applicable statute and current procedural authority.
Historical Dictionary Support
Bouvier's Law Dictionary addresses the topic concisely, anchoring the rule in judicial notice doctrine and illustrating it with the Sunday process example drawn from Fortescue and Strange — two eighteenth-century English reporters. Bouvier's treatment reflects the common law baseline: the rule was not controversial, courts simply knew what day it was, and errors as to prohibited days produced procedural defects. What Bouvier's does not address — and what modern researchers must supply from other sources — is the layered complexity introduced by statutory deadline rules, the distinction between Sunday as a dies non and Saturday as a half-day in some jurisdictions, and the treatment of federal and state holidays as additional non-judicial days. Historical dictionaries generally treat days of the week as a procedural footnote rather than a substantive doctrine, which understates how frequently day-of-the-week questions arise in deadline litigation.
Jurisdictional Note
Sunday laws varied significantly among the states and were subject to constitutional challenge under First and Fourteenth Amendment theories throughout the twentieth century. Many state Sunday restrictions on legal process have been repealed or limited by statute. Federal practice is governed by FRCP 6 and equivalent provisions in the criminal and appellate rules, which treat Sundays and legal holidays uniformly for deadline-extension purposes.
Encyclopedia Cross-Reference
The Law Mind Tax Encyclopedia: IRS Notice of Deficiency 90-Day Letter — for the specific application of day-counting rules to the Tax Court petition deadline.
The Law Mind Immigration Law Encyclopedia: Federal Court Review — Standard of Review, Exhaustion, and the 30-Day Filing Deadline — for day-counting in the context of immigration petition deadlines.