Definition
Mortis causa is a Latin phrase meaning "by reason of death" or "in contemplation of death." It describes acts, transfers, or dispositions made in anticipation of the maker's imminent death. The phrase functions primarily as a modifier rather than a standalone legal concept — its meaning is realized through compound terms, most importantly donatio mortis causa (a gift made in contemplation of death).
In its core application, a transaction or instrument made mortis causa is one conditioned on the maker's death. If the maker survives the anticipated peril, the transaction is typically revocable or void. If death follows, the transfer becomes effective. This conditionality is what distinguishes mortis causa dispositions from ordinary inter vivos (lifetime) gifts and from testamentary instruments executed under formal will requirements.
The phrase is also encountered in procedural and evidentiary contexts — most notably in the "dying declarations" doctrine, where statements made mortis causa (in awareness of impending death) carry special evidentiary weight at common law.
---
Common Confusion
Mortis causa is frequently paired with, and confused against, its counterpart: inter vivos, meaning "between the living" or "during life." The distinction matters because inter vivos gifts are irrevocable upon delivery and acceptance, while gifts mortis causa remain revocable during the donor's lifetime and are automatically revoked if the donor recovers. A second point of confusion arises between donatio mortis causa and a testamentary bequest. Both transfer property at death, but a donatio mortis causa requires no will formalities — it operates as a conditional gift completed by death, not as a testamentary instrument. Courts have sometimes blurred this line, and historical sources occasionally treat the two as functionally equivalent, which they are not.
---
Why It Matters in Research
The phrase mortis causa rarely appears in isolation in case law or statutes. Researchers should treat it as a locator signal pointing to the doctrine of donatio mortis causa, which carries its own substantial body of case law and treatise commentary. Searching for mortis causa alone in historical reporters will surface discussions of gifts, but also incidental uses in probate proceedings, evidentiary rulings on dying declarations, and occasionally in civil law materials where the phrase carries broader application.
A critical research trap: in many 19th-century American decisions, courts conflate donatio mortis causa with testamentary disposition, requiring will formalities the doctrine was never intended to demand. This tension produced inconsistent outcomes across jurisdictions, and a researcher reading early American cases without this context may incorrectly conclude the doctrine was stricter than it actually was under English equity.
The phrase also appears in the civil law tradition with a somewhat broader scope — causa mortis in Roman law and its civil law successors encompasses not just gifts but other transactions conditioned on death (certain contracts, legacies, manumissions). Researchers working in Louisiana, Quebec, or comparative law contexts should not assume the common law meaning of donatio mortis causa exhausts the civil law content of the term.
Corpus connections: this term links directly to donatio mortis causa entries, inter vivos gift doctrine, delivery requirements in property law, and the dying declarations exception in evidence. Researchers moving from mortis causa into gift law will need to engage delivery and intent elements carefully — these are the primary grounds on which mortis causa gifts are challenged.
---
Historical Dictionary Support
Both editions of Black's define the phrase identically in substance: "by reason of death; in contemplation of death," with immediate cross-reference to donatio mortis causa as the operative legal application. The second edition adds the citation to Terrill v. Public Adm'r, 4 Bradf. Sur. (N.Y.) 245, 250, for the maxim "Mortis momentum est ultimum vitæ momentum" — the last moment of life is the moment of death — a formulation relevant to timing disputes in gift and inheritance cases.
Neither edition develops the term beyond its function as a phrase modifier. This reflects the historical dictionary treatment generally: mortis causa is defined as a gateway to donatio mortis causa, not as a freestanding doctrine. Researchers relying solely on these definitions will find the phrase explained but not the doctrine fully developed. The real substance sits in the donatio mortis causa entry and in the treatise and case law it generates.
What historical sources do not address is the civil law dimension or the evidentiary use of the phrase in dying declarations doctrine — both of which a modern researcher may encounter and which require sources beyond Black's.
---
Encyclopedia Cross-Reference
Property Law — Personal Property: Gifts (Inter Vivos, Causa Mortis — Delivery, Intent, Acceptance)
---