Definition
Commorientes (Latin: "those who die together") refers to two or more persons who die simultaneously, or under circumstances in which the order of their deaths cannot be determined. The term most commonly arises in succession, inheritance, and insurance law, where the sequence of deaths controls the disposition of property. If a testator and a beneficiary both perish in the same disaster — a shipwreck, a fire, a plane crash — and no evidence establishes who survived the other, even briefly, the law must adopt a rule for how to handle the resulting uncertainty.
The practical problem is this: if A leaves property to B, and both die together, did B ever acquire the property (and thus pass it to B's heirs), or did A die last (passing the property along A's own line of succession)? The answer turns entirely on assumed or proven order of death.
Common Confusion
Commorientes is sometimes confused with the concept of survivorship. They are related but distinct: survivorship is the legal principle that determines what happens when one person outlives another; commorientes describes the factual condition — simultaneous or unascertainable death — that triggers survivorship rules or their alternatives. The commorientes doctrine is the problem; survivorship statutes are one solution.
Why It Matters in Research
The central research trap is jurisdictional divergence in how the presumption of simultaneous death is resolved. Historically, English common law declined to presume any order of death among commorientes, with the result that no survivorship was assumed and property passed as if neither had survived the other. Civil law systems, by contrast, sometimes employed age-based or sex-based presumptions to infer order of death when evidence was absent — presumptions a researcher will encounter in older treatises and continental sources.
In American practice, the Uniform Simultaneous Death Act (1940, revised 1993) displaced the common law uncertainty by establishing that each person is treated as having predeceased the other for purposes of that person's own property — effectively splitting the estate along each decedent's line. Many states have enacted variants. The Uniform Probate Code addresses the same problem through a 120-hour survivorship requirement: a beneficiary must survive the decedent by 120 hours to take under the will or intestacy, collapsing the commorientes problem into a defined time threshold.
Researchers working with historical American sources — particularly pre-1940 wills litigation — will encounter extensive uncertainty about which rule applied in a given jurisdiction, since courts were not uniform. Researchers working in insurance law will find a parallel track: life insurance policies often contained their own survivorship clauses, and policy language rather than statute frequently governed the outcome.
The term also appears in conflict-of-laws contexts, since the applicable presumption may vary depending on whether the law of the domicile, the situs of the property, or the place of death controls.
Historical Dictionary Support
The historical dictionaries are largely in agreement on the core meaning — persons dying simultaneously from a common calamity — but vary in depth. Burrill is the most useful for research, citing directly to the Digest (Dig. 34.5) and to Kent's Commentaries, confirming that the doctrine has civil law roots. The Digest passages Burrill references (Dig. 34.5.8, 9, 16, 22, 23) address the Roman rules on order of death among relatives, including the age and sex presumptions that civil law applied when simultaneous death was unresolvable. Burrill also notes the synonym pariter mortui ("equally dead"), a term a researcher may encounter in older Latin-language or civilian sources.
Rapalje & Lawrence adds an important observation the other dictionaries omit: that neither English nor American law had settled the question at the time of writing — an honest acknowledgment that the doctrine was genuinely unresolved, not merely technical. This makes Rapalje & Lawrence's entry a useful marker of the pre-statutory uncertainty.
Black's (both editions) and Bouvier's offer minimal entries, functioning as cross-references to survivorship rather than independent analysis. Anderson confirms the civil law origin with the "L." designation but adds nothing beyond the bare definition.
What the historical dictionaries collectively miss: the statutory revolution. None of them anticipate the Uniform Acts, and a researcher relying solely on these sources will not understand modern American practice without supplementing with statutory materials.
Jurisdictional Note
American jurisdictions are now largely governed by either the Uniform Simultaneous Death Act, the Uniform Probate Code's 120-hour rule, or state-specific statutory variants. Civil law jurisdictions historically employed presumptions based on age and sex that have no American common law counterpart. Researchers working across common law and civil law systems should not assume the same default rules apply.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Inheritance and Succession Law; Survivorship and Simultaneous Death