Definition
A Latin term from Roman and common law tradition meaning omission, or a leaving out. In legal usage, omissio refers to the failure to include, mention, or perform something — whether in a written instrument, pleading, or legal obligation. The term appears most often in maxim-based reasoning, where courts and commentators addressed the legal consequences (or non-consequences) of things left unstated in documents or proceedings.
The term is closely associated with the maxim: Omissio eorum quae tacite insunt nihil operatur — "The omission of those things which are tacitly implied is of no consequence." This principle holds that when something is legally implied by the nature of a transaction, instrument, or status, the failure to state it expressly does not invalidate the instrument or defeat the implication. What the law reads in, the parties need not write out.
Common Confusion
Omissio should not be confused with the broader concept of omission in modern tort or criminal law, where an omission refers to a failure to act that may give rise to liability. The Latin term omissio as used in historical legal sources is narrower and more specifically tied to questions of drafting and documentary construction — the leaving-out of words or provisions — rather than to conduct-based failures to act. A researcher encountering omissio in an older treatise or case report is likely in the territory of instrument interpretation, not duty-breach analysis.
Why It Matters in Research
Omissio appears in the Law Mind corpus primarily in the context of Latin maxims and their application to the construction of deeds, contracts, grants, and pleadings. Its practical significance lies almost entirely in the maxim with which it travels: the principle that implied terms need not be stated, and that silence as to an implied matter does not amount to exclusion.
Researchers working in early common law sources — Year Books, Coke, Plowden, and their successors — will encounter this principle applied to conveyances (where the omission of a standard clause did not defeat an implied covenant), to grants of authority (where unstated incidents attached by operation of law), and to pleadings (where omissions of matter that was necessarily implied were treated as harmless).
The key trap in historical sources is scope-creep in application. Courts sometimes cited the omissio maxim broadly, using it to supply missing terms that were arguably not "tacitly implied" at all but merely convenient. Researchers should distinguish between the maxim's legitimate application (omission of legally implied incidents) and its use as a judicial gap-filling device without clear grounding in implication.
This term connects directly to research on the construction of instruments, implied covenants, the cy-pres doctrine in equity (where defective expression is cured by reference to intent), and the general common law treatment of surplusage and implied terms. It also intersects with pleading history, where the distinction between fatal omissions and harmless omissions was a recurring problem in the old common law forms of action.
Historical Dictionary Support
Burrill's Law Dictionary defines omissio simply and accurately: "Omission; a leaving out," with the maxim following as illustration. The entry is brief and primarily translational, pointing researchers toward the maxim rather than developing the term as an independent concept.
Burrill cites 2 Bulstrode 131 in support of the maxim, which is a real and traceable seventeenth-century English report. This citation grounds the term firmly in the common law reporters, confirming that omissio was not merely a civilian borrowing but was actively deployed in English court reasoning.
The historical dictionaries offer limited analytical development here. Burrill gives the reader the term, its root, its translation, and the maxim — which is sufficient for identification but leaves the substantive doctrine undeveloped. Researchers should supplement with treatise sources (Coke's commentary, or later works on the construction of deeds) to understand the full operational context of the principle.