Definition
In law, "life" carries several distinct meanings depending on context.
1. Biological life (general). The state of a human being or other organism in which natural functions are performed and organs are capable of functioning. For most legal purposes, human life is treated as a continuous state that begins at some legally defined point and ends at death.
2. Legal personhood and the duration of rights. Life, in the sense of a living person's legal existence, defines the period during which a natural person may hold rights, incur obligations, and be a party to legal transactions. Many legal instruments — wills, trusts, life estates, annuities — are measured by a person's life, making the precise beginning and end of life a matter of legal consequence, not merely biological fact.
3. Life as a legally protected interest. Life is one of the fundamental interests protected by constitutional due process and by the common law of homicide, personal injury, and wrongful death. The legal system assigns legal significance to the taking of life (criminal law), the accidental loss of life (tort law), and the anticipated duration of life (actuarial calculations in damages, insurance, and pension law).
4. Life in instruments and estates. A life estate grants rights measured by the duration of a specified person's life. Contracts and trusts may similarly run "for life," meaning they expire at death. The term "life tenant" and the concept of a measuring life in the rule against perpetuities both depend on "life" as a temporal unit.
Common Language
Modern common usage (Wiktionary): Principally defined in its biological sense — the state of living organisms — with secondary senses in philosophy, biography, and everyday speech.
Historical common usage (Webster's 1913): "The state of being which begins with generation, birth, or germination, and ends with death; also, the time during which this state continues; that state of an animal or plant in which all or any of its organs are capable of performing all or any of their functions."
The common and legal meanings substantially overlap in their biological core, but law requires precision the ordinary word does not. Specifically, law must fix the moment life begins and ends for purposes of rights, liability, and measurement — questions ordinary usage leaves open. A layperson speaking of "life" assumes its boundaries are obvious; legal sources reveal they are contested and jurisdiction-dependent.
Common Confusion
Life (biological existence) vs. life (duration / measuring life): In ordinary speech, "life" refers to the state of being alive. In instruments and property law, "life" often functions as a unit of time — a measuring life in the rule against perpetuities need not even be the life of a party to the transaction. These two uses can produce confusion when reading historical deeds, trusts, or statutes.
Legal beginning of life vs. biological beginning of life: Historical legal sources placed the commencement of legal personhood at quickening (first perceived fetal movement), a threshold that no longer governs in most modern jurisdictions. Researchers reading pre-twentieth-century legal texts will encounter "life" commencing at a point different from both modern law and modern biology.
Core Elements
Because "life" in law functions across multiple doctrinal contexts, its operative legal content depends on the framework:
Criminal law: Life is the protected interest whose unlawful taking constitutes homicide. The definition of when life begins and ends has direct bearing on the scope of homicide statutes, feticide statutes, and laws governing end-of-life decisions.
Property and estates: Life serves as a measuring unit. A life estate endures for the life of a specified person (the measuring life). The rule against perpetuities limits future interests to those that must vest within a life in being plus twenty-one years. Here, "life" is a temporal concept as much as a biological one.
Insurance law: "Life" defines the subject matter and duration of a life insurance contract. Whether an insured was alive at the time of policy issuance, and the moment of death as the triggering event for proceeds, are both legal determinations. Proceeds received because of the death of the insured are generally excludable from gross income under federal tax law — see the Encyclopedia cross-reference below.
Tort law: Loss of life generates wrongful death claims and survival actions. Life expectancy, calculated actuarially, determines the measure of economic damages.
Constitutional law: "Life" appears as the first-listed protected interest in the Due Process Clauses of the Fifth and Fourteenth Amendments, establishing it as a baseline against which government deprivation must be justified.
Why It Matters in Research
Researchers encounter "life" across nearly every area of law, but several traps deserve attention.
The beginning of life has shifted dramatically. Bouvier's placed legal life as commencing at quickening; Black's incorporated both the physiological definition and Bichat's formulation ("the sum of the forces by which death is resisted"). Neither maps cleanly onto modern statutory or constitutional frameworks. When reading historical materials on homicide, inheritance by unborn children, or abortion-adjacent law, note which threshold the source applies — quickening, conception, viability, or birth — because the answer changes the legal outcome.
"Life in being" is a technical term of art in the rule against perpetuities and should not be read as simply meaning "a person who is alive." It has a specific historical construction and has been modified or abolished in many jurisdictions by statute (Uniform Statutory Rule Against Perpetuities) or wait-and-see doctrine.
Life insurance proceeds receive special tax treatment. The intersection of "life" as the insured interest and "life" as the duration of the policy creates a body of tax law that is not intuitive. The Law Mind Tax Encyclopedia entry on Exclusions — Life Insurance Proceeds is the recommended starting point for corpus research in this area.
Historical sources vary in their engagement with the death side of the equation as much as the birth side. The development of brain-death standards and statutory definitions of death (the Uniform Determination of Death Act) substantially altered the legal endpoint of "life" in the twentieth century. Pre-UDDA materials should be read with this in mind.
Historical Dictionary Support
The historical dictionaries converge on the biological core: life is the state in which an organism's organs perform their natural functions. Black's (both editions) incorporates this formulation almost verbatim from Webster, then adds Bichat's philosophical gloss — "the sum of the forces by which death is resisted" — which Bouvier also quotes. The agreement is notable: legal dictionaries of the nineteenth century were content to borrow the biological definition wholesale rather than construct an autonomous legal one.
Bouvier goes further than the others by addressing the legal commencement of life directly, fixing it at quickening and citing Blackstone and Coke. This is the entry most useful for historical research into criminal law and the rights of unborn children in the common law period. Bouvier's note that "physiology pronounces life as existing from the period of" — the entry is cut off in the source — suggests awareness that the legal and biological thresholds were already diverging in his era.
Rapalje & Lawrence and Anderson's entries retrieved under this term appear to be mismatched (their content addresses maritime liens and lien law generally), suggesting indexing artifacts in the corpus for this term. Researchers should not rely on those entries for the meaning of "life."
What the historical dictionaries uniformly omit: constitutional dimensions, tax treatment, actuarial damages calculations, and the rule against perpetuities use of "life in being." These are areas where modern secondary sources and the Law Mind Encyclopedia are essential supplements.
Jurisdictional Note
The legal definition of when life begins and ends varies significantly by jurisdiction and statutory context. Wrongful death statutes differ in whether they recognize claims for the death of a viable fetus. End-of-life determinations are governed by state law, and while the Uniform Determination of Death Act has been widely adopted, its implementation varies. Constitutional questions about deprivation of life trigger federal standards, but the underlying substantive definitions often remain state-law questions.
Encyclopedia Cross-Reference
Exclusions — Life Insurance Proceeds (The Law Mind Tax Encyclopedia): Covers the federal income tax treatment of proceeds received by reason of the death of an insured under a life insurance contract, including the general exclusion rule, exceptions, and transfer-for-value issues.