Definition
Incertitudo (Latin; also rendered as incertus, incerta, incertum) is a term from old English law and Roman-derived civil law meaning uncertainty, doubt, or want of certainty. It appears in medieval and early modern legal texts to describe conditions where a person, fact, right, or legal status is unknown, indeterminate, or incapable of precise ascertainment.
The related adjective incertus carries the same core meaning: uncertain, doubtful, not known. The maxim preserved in Burrill — incertus possessor est quem ignoramus, "an uncertain possessor is one whom we do not know" — illustrates the term's practical application in property and possessory contexts, where the identity of a holder or claimant could not be established with legal sufficiency.
Incertitudo functioned less as a standalone cause of action or defense and more as a descriptive legal condition — a defect in proof, pleading, identification, or instrument that rendered a legal proceeding or claim legally insufficient or void.
Common Confusion
Incertitudo should not be confused with ambiguitas, the Latin term for ambiguity in written instruments. Ambiguitas concerns unclear or double meaning in language already expressed; incertitudo is the broader condition of something simply being unknown or unascertained — including persons, facts, and possessory status, not only textual meaning. Historical sources sometimes use the terms in proximity, but they address distinct defects. A drafter who writes an unclear clause creates ambiguitas; a document that fails to identify any grantee at all presents incertitudo.
Why It Matters in Research
Researchers will encounter incertitudo primarily in Latin-heavy medieval and early modern legal texts — Fleta, Bracton, and glossed civil law materials — rather than in modern case law or statutory codes. The term did not survive as an active term of art into modern common law practice; its function was absorbed into doctrines of uncertainty in contracts, void grants, and pleading sufficiency.
Key research traps:
First, the term appears in abbreviated or declined Latin forms (incertus, incerta, incertum), which can make keyword searching unreliable. Researchers working in digitized editions of Fleta or similar sources should search across all grammatical forms.
Second, Burrill cites Fleta, lib. 4, c. 17, § 1 as the authority. Fleta is a late-thirteenth-century English legal treatise of uncertain authorship, modeled on Bracton. Researchers using this citation should be aware that Fleta editions vary in their chapter and section numbering depending on the edition consulted, and cross-referencing with a reliable modern edition (such as the Selden Society edition) is advisable.
Third, in property and possessory research, the maxim incertus possessor est quem ignoramus connects incertitudo to questions of seisin, unascertained heirs, and the identity of claimants in real actions. This link is productive for researchers tracing the history of certainty requirements in conveyancing and the common law treatment of void versus voidable grants.
Fourth, in the civil law tradition (which influenced English ecclesiastical and admiralty courts), incertitudo had a broader application across persons, things, and obligations. Researchers working in equity or admiralty records may find the term used more expansively than in common law pleading contexts.
Historical Dictionary Support
Burrill's Law Dictionary is the primary English-language legal dictionary source that defines incertitudo as a standalone entry, glossing it simply as "uncertainty" with the Fleta citation. Burrill separately enters incertus and supplies the maxim regarding uncertain possession, treating the adjective and the noun as related but distinct entries.
Burrill's treatment is characteristically spare — he identifies the source and supplies the core meaning without extended analysis. What his entry does not address is the doctrinal consequence of incertitudo: when, for instance, uncertainty as to a possessor rendered a claim legally insufficient, or how the concept interfaced with the developing common law rules on certainty of parties in pleading. Researchers should treat Burrill here as a pointer to primary sources rather than a complete account.
No entry for incertitudo appears in Black's Law Dictionary (early editions), Tomlin's Law Dictionary, or Bouvier's Law Dictionary under this exact heading, which suggests the term was recognized primarily by civil-law-oriented lexicographers rather than those focused on common law practice.
Jurisdictional Note
Incertitudo as a term of art belongs to the historical legal vocabulary of medieval English common law and the civil law tradition that influenced ecclesiastical and admiralty courts. It has no active presence in modern American, English, or Commonwealth legal usage. Researchers in civilian jurisdictions (Scotland, Louisiana, Quebec) with strong Roman law roots may find parallel concepts under analogous Latin or vernacular terms in their own sources.