Definition
A Latin term meaning "certain," "definite," "known," or "determined." In legal usage, certum describes something fixed, ascertainable, or reduced to a precise standard — most commonly applied to sums of money, quantities, or obligations that are either already specific or capable of being made specific by calculation or proof.
The term appears most often in the maxim certum est quod certum reddi potest: "That is certain which can be made certain." This principle holds that an obligation or amount need not be stated with explicit precision at the outset, provided it is capable of being computed or established by reference to an agreed standard, external evidence, or legal formula. The practical effect is that courts will treat an apparently indefinite obligation as sufficiently certain if certainty can be derived from testimony, computation, or the surrounding circumstances.
Common Confusion
Certum and its associated maxim are sometimes conflated with the broader doctrine of contractual certainty — the rule that vague or indefinite agreements may be unenforceable. The maxim does not nullify that doctrine; it qualifies it. An obligation is not automatically void for want of facial precision. If the means to arrive at a definite figure already exist in the record or by operation of standard computation, courts applying the certum principle will treat the obligation as sufficiently determinate. The confusion matters most in historical sources, where writers invoke certum to resolve ambiguity that modern courts might address under different analytical frameworks.
Why It Matters in Research
Researchers encounter certum primarily in two contexts: (1) cases and treatises addressing the enforceability of obligations expressed in general or approximate terms — particularly negotiable instruments, liquidated damages clauses, and rent or annuity obligations — and (2) maxim collections and Latin glossaries embedded in common law treatises, where the term appears without extended analysis.
The practical danger in historical sources is taking certum as a blanket license for indefiniteness. Older treatise writers cited the maxim to rescue obligations that were computationally certain even if facially ambiguous; they did not use it to validate genuinely vague agreements. A researcher who reads historical invocations of certum est quod certum reddi potest without attention to that limiting context may overread the doctrine's scope.
Jurisdictional variation is less a concern here than temporal variation. The maxim was central to common law reasoning about commercial paper and rent obligations in the eighteenth and nineteenth centuries. Modern commercial law has largely absorbed and codified its logic — particularly in the treatment of variable-rate or formula-based obligations — so the maxim appears less frequently in contemporary opinions, though it remains available as interpretive authority in courts that still engage with Latin maxims.
When tracing a line of authority invoking certum, researchers should note that Coke's reports are the most frequently cited historical anchor (Burrill points to Co. 30 and Co. Litt. 96a), meaning the analytical chain runs through English common law sources before reaching American adoption. Colonial and early federal sources may cite the maxim without independent analysis, simply importing Coke's authority.
Historical Dictionary Support
Anderson and Burrill are in agreement on the core definition: certum means "certain," and the term's legal significance turns almost entirely on the maxim certum est quod certum reddi potest. Both sources treat this as a well-settled principle rather than a contested one.
Anderson's entry is the more practically useful of the two. It situates the maxim in context — specifying that when the law requires certainty, that which can be shown to be certain by computation or testimony satisfies the requirement — and offers concrete illustrations involving negotiable instruments and liquidated damages. This is the entry to begin with when advising on research into specific commercial or contractual disputes.
Burrill's entry is briefer and more purely referential, cross-directing the reader to "Certain" and attaching the maxim with a citation to Coke (9 Co. 30; Co. Litt. 96a) and a quotation attributed to Lord Ellenborough that appears truncated in the available text. Burrill's value here is the citation trail to English authority rather than independent analysis. Researchers should note that Burrill's entry also includes a stray entry for cervus (stag or deer) in the same block of text — an artifact of the dictionary's alphabetical proximity, not a related legal concept.
Neither dictionary addresses modern statutory codifications of the certainty principle, which is expected given their dates of publication. Neither engages with civil law treatments of certum, where the concept has a distinct but related lineage in Roman law concerning obligationes certi and the condictio certi. Researchers working in mixed jurisdictions or civil law contexts should not rely on Anderson or Burrill for that tradition.
Jurisdictional Note
The certum maxim was received into American common law as part of the general inheritance of English common law doctrine. Its application varies more by subject matter than by state: courts addressing negotiable instruments, rent obligations, and damages calculations have been its primary users. Civil law jurisdictions applying their own certainty doctrines may reach similar results by different analytical paths.