Definition
Uncertainty, in law, refers to a want of definiteness or precision in the terms of a legal instrument, obligation, or legal description such that its meaning, scope, or application cannot be determined with sufficient clarity to be enforced or given effect. The concept arises across multiple legal contexts—contracts, wills, deeds, pleadings, and grants—where vagueness in expression may render the whole or part of the instrument void or ineffective.
1. In contracts and wills: A provision so indefinite in its terms that no court can ascertain what the parties intended, what performance is required, or who is to receive a benefit. Uncertainty of this degree is fatal to enforcement.
2. In conveyances and grants: A description of land or property so vague that the subject matter of the grant cannot be identified. Historically distinguished from mere ambiguity, which might be resolved by extrinsic evidence, as opposed to uncertainty, which admits of no such cure.
3. In pleading: A failure in a complaint, indictment, or other pleading to state the facts with sufficient precision to apprise the opposing party of the charge or claim, or to define the issue for trial.
Common Language
Modern common usage (Wiktionary): The state of being uncertain; lack of certainty; doubt about whether something is true, will happen, or what will happen.
Historical common usage (Webster's 1913): The quality or state of being uncertain; doubtfulness; dubiousness; hesitancy; as, the uncertainty of some future event.
The gap between ordinary and legal usage is meaningful. In common speech, uncertainty describes a subjective mental state—a person is uncertain when they lack confidence or information. In law, uncertainty is an objective quality of the instrument itself. A drafter may be perfectly confident in their intent, yet the document may still be legally uncertain if that intent cannot be extracted and applied by a court. Legal uncertainty is a defect in expression, not in the mind of the author.
Common Confusion
Uncertainty is frequently conflated with ambiguity, but the two carry distinct legal consequences. Ambiguity arises when language is susceptible to two or more reasonable meanings—the instrument says something, but it says it in a way that points in multiple directions. Uncertainty arises when language fails to say anything definite at all. Ambiguity invites interpretation and often survives with the aid of extrinsic evidence or rules of construction. Uncertainty, in its strong form, cannot be resolved by evidence because there is no intelligible meaning to clarify. The practical consequence is significant: a court that finds ambiguity will proceed to construe; a court that finds radical uncertainty may simply void the provision.
Why It Matters in Research
Researchers encounter uncertainty as both a doctrine and a defect-label in very different bodies of law, and conflating these contexts leads to misreading sources. In contract law, the doctrine evolved alongside the consideration and definiteness requirements—nineteenth-century treatises discuss uncertainty primarily as a contracts defect, and cases from that era often use uncertainty and indefiniteness interchangeably without the precision modern doctrine applies. In wills and testamentary law, courts developed a more nuanced vocabulary: uncertainty of subject (what is given), uncertainty of object (to whom it is given), and uncertainty of quantity (how much). These subcategories appear in equity and probate materials from the eighteenth century forward, and the distinctions matter when reading older chancery decisions.
In conveyancing, uncertainty in land descriptions is a recurring source of litigation well into the twentieth century, particularly in American frontier-era grants and Spanish and Mexican land patents, where survey descriptions were imprecise. Researchers working in those areas should note that the legal standard for sufficient certainty of description has varied by jurisdiction and era.
The term also appears in pleading practice under common law where uncertainty was a ground for special demurrer—a procedural posture that has largely disappeared under modern notice-pleading regimes. Historical pleading manuals treat uncertainty as a technical defect with specific cures; this usage is largely obsolete and can mislead researchers who encounter it in nineteenth-century practice guides.
Historical Dictionary Support
Rapalje & Lawrence define uncertainty as "the want of certainty; indefiniteness," and organize their treatment around the distinction between uncertainty of language and uncertainty of subject matter, noting that the former may sometimes be aided by construction while the latter cannot. They reflect the dominant mid-to-late nineteenth-century view that legal instruments must be sufficiently definite that "a court can see what is to be done" and by whom—a formulation that tracks the specific performance standard familiar in equity. Their entry correctly identifies pleading as a separate field of application but does not develop the will and testamentary context in depth, an omission consistent with the period's relative underemphasis of probate doctrine in general law dictionaries.
What Rapalje & Lawrence do not capture is the later doctrinal refinement—particularly in twentieth-century American contract law—where uncertainty came to be treated as a distinct element of contract formation analysis, separate from both consideration and capacity, and addressed explicitly in the Restatement frameworks.
Jurisdictional Note
The consequences of uncertainty vary between law and equity traditions, and between American and English practice. English courts of equity developed more elaborate tools for resolving apparent uncertainty in trust and will instruments than common law courts applied to contracts. In American jurisdictions, the willingness to apply the cy-pres doctrine and charitable trust construction principles can rescue instruments that would otherwise fail for uncertainty of object.