Definition
A Latin maxim meaning "we can" or "we are able." In legal usage, the term appears most commonly in the maxim *Id possumus quod de jure possumus* — "We can do that which we can do by law." The principle holds that legal capacity to act is not equivalent to mere physical ability to act. When the law speaks of what a person or entity "can" do, it refers exclusively to what is lawfully permissible, not what is physically or practically possible.
Common Confusion
The maxim addresses a persistent conflation between physical capability and legal authority. That a party has the power, means, or opportunity to do something does not mean the law recognizes or permits that act. POSSUMUS, as used in legal argument, always imports the qualifier *de jure* — by right or by law — even when that qualifier is left unstated. Researchers should be careful not to read maxims using "can" or "may" in purely descriptive terms when the legal tradition treats them as normative claims about lawful capacity.
Why It Matters in Research
POSSUMUS appears in historical legal argument as a foundational principle for limiting the reach of claimed powers — whether of private parties, corporations, or public officials. Its significance lies not in any standalone doctrine but in its function as a maxim of construction: it constrains how courts and counsel read grants of authority. When a charter, statute, or contract says a party "may" or "can" do something, the maxim supplies an implicit ceiling — the grant of ability is a grant only of lawful ability.
Researchers working with early common law sources, ecclesiastical law texts, or equity treatises will encounter this maxim most frequently in disputes over the scope of delegated authority. It recurs in arguments about whether an act done without legal right is nonetheless valid because it was physically accomplished. The consistent answer in the tradition is no — legal consequence follows legal capacity, not brute fact.
The maxim also appears in discussions of contracts and obligations: a party cannot excuse performance by claiming incapacity if the incapacity is self-induced or if the law otherwise imposes the duty regardless of physical difficulty.
Historical Dictionary Support
Burrill's Law Dictionary traces POSSUMUS directly to the Latin *possum/posse* and quotes the maxim *Id possumus quod de jure possumus* with a citation to Lane, 116. Burrill's gloss is concise and accurate: "When we speak of what we can do, we mean what we can do lawfully. Mere physical ability to do an act is not regarded in law." This formulation captures the maxim's entire operative force.
Historical dictionaries offer little beyond this condensed treatment because POSSUMUS functions primarily as a building block of larger maxims rather than as an independent legal concept. The term is not separately developed in Bouvier or Black's early editions with notable elaboration. Researchers should treat Burrill's entry as the representative source and look to the maxim itself — and the cases and treatises applying it — for substantive development.