Definition
A Latin maxim appearing in three related forms, each expressing the same foundational legal principle: that a valid legal transaction — whether a gift, a judgment, or a sale — requires its subject matter to be certain and definite. The full phrases and their meanings are:
1. Oportet quod certa res deducatur in donationem — "It is necessary that a certain thing be brought into the gift." A conveyance or gift is invalid unless its object is sufficiently identified.
2. Oportet quod certa res deducatur in judicium — "A thing certain must be brought to judgment." A legal proceeding must have a definite subject matter; a judgment cannot be rendered on something wholly indefinite.
3. Oportet quod certa sit res quae venditur — "It is necessary that there should be a certain thing which is sold." A contract of sale requires an ascertainable subject matter to be binding.
Collectively, these maxims state a principle of legal certainty: no legal obligation, transfer, or adjudication can attach to something undefined or undetermined. The subject matter must be capable of being identified before the law can give effect to the transaction.
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Why It Matters in Research
This maxim appears in a cluster of related certainty-of-subject-matter problems that recur across property law, contract law, and pleading. Researchers encountering it in early common law sources should understand it as a doctrinal anchor — not an isolated rule — supporting a much broader principle that runs through gifts, sales, and judgments alike.
In older property and conveyancing texts, the donation form of the maxim (deducatur in donationem) traces directly to Bracton (fol. 150), making it a medieval source. Researchers working in that period should treat the Bracton citation as authoritative context; the maxim reflects Roman-influenced civil law doctrine absorbed into English common law through Bracton's synthesis. It should not be read as a purely statutory or common law rule developed by English courts independently.
The judgment form (deducatur in judicium), cited to Jenkins' Centuries (Jenk. Cent. 84), is relevant to early pleading research. It corresponds to the requirement of certainty in declaring the subject of a claim — a theme visible in the formal requirements of common law writs and later in the certainty rules of equity pleading.
The sales form (certa sit res quae venditur) connects directly to contract law's requirement that subject matter be sufficiently definite to support enforcement — a doctrine that persists in modern contract law as the definiteness requirement, though modern sources no longer rely on the Latin formulation.
Trap for researchers: Black's 2nd Edition truncates the sales entry mid-sentence ("To make a valid s—"), indicating the source text was cut off. Any research relying on this maxim for the sale-of-goods context should not treat Black's 2nd Edition as a complete statement of the rule. Consult Bracton, Coke's works, or civilian sources for fuller treatment.
These three forms are frequently grouped together in digest-style presentations precisely because they express a unified principle across transaction types. A researcher finding one form in a source should search for the others — they often appear in proximity.
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Historical Dictionary Support
Black's Law Dictionary (2nd Edition) presents all three forms consecutively, treating them as a family of related maxims rather than distinct rules. This is the appropriate framing. The first form is attributed to Bracton (fol. 150), grounding it firmly in the medieval civilian tradition. The second is attributed to Jenkins' Centuries, a 17th-century collection of common law cases and maxims. The third entry is unfortunately incomplete in Black's, ending mid-explanation.
No competing historical dictionary definitions are available in the source material for this entry. Researchers should note that the Bracton attribution makes this a maxim with genuine doctrinal lineage, not a later invented formulation. It is not a "brocard" of uncertain origin — it has traceable, citable roots.
What the historical dictionary record does not provide is any explanation of how these maxims were applied or limited in practice. The entries are pure maxim-form: Latin text plus translation. For application, primary sources (Bracton, Jenkins) must be consulted directly.
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