Definition
A perpetuity, in its primary legal sense, is a disposition of property — by deed, will, or trust — that attempts to postpone the vesting of an interest beyond the period permitted by law. Because such arrangements effectively remove property from commerce and free alienability for an indefinite or excessive time, the law treats them as contrary to public policy and, in jurisdictions that retain the traditional rule, voids the offending limitation.
The term carries two distinct but related meanings in legal usage:
1. The offending limitation itself. A future interest — whether a remainder, executory interest, or other limitation — is a perpetuity when it is not certain to vest, if it vests at all, within the period prescribed by the Rule Against Perpetuities: a life or lives in being at the creation of the interest, plus twenty-one years, with a further allowance for gestation. The focus is not on whether the arrangement will actually last forever, but on whether it might vest too remotely. An interest that could theoretically vest one day outside the permitted period is void from the outset under the traditional rule, regardless of how unlikely that result is in practice.
2. The inalienable estate or fund. Perpetuity also describes the condition of property itself when it has been effectively locked out of commerce — rendered inalienable — for longer than the law allows. In this sense the word refers not to the limiting instrument but to the resulting state of the property.
A third, narrower usage appears in financial and mathematical contexts: a perpetuity is an annuity structured to pay an indefinite series of periodic payments with no terminal date. This usage is common in finance and occasionally appears in legal instruments such as endowments or charitable trust funding arrangements.
Common Language
Modern common usage (Wiktionary): "The quality or state of being perpetual; endless duration; uninterrupted existence." Also, loosely, something that lasts forever or feels as though it does.
Historical common usage (Webster's 1913): "The quality or state of being perpetual"; also the period of years in which simple interest equals the principal — already showing the financial calculation sense.
The gap matters for researchers. In ordinary English, perpetuity means simply endless continuation. In law, the word is almost always a term of condemnation: something structured to last forever is precisely what the rule prohibits. A legal instrument described as creating a "perpetuity" is not being praised for its durability — it is being identified as void or voidable. Researchers encountering the word in older equity opinions should read it as a signal of invalidity, not longevity.
Common Confusion
Perpetuity vs. the Rule Against Perpetuities. The perpetuity is the offending interest; the Rule Against Perpetuities (RAP) is the legal doctrine that invalidates it. The two are not interchangeable, though historical sources sometimes use the term loosely. An interest violates the RAP; the resulting limitation is the perpetuity. Researchers should also distinguish a void perpetuity from a merely long-duration trust or charitable endowment, which may lawfully last for a very long time without violating the rule if interests vest within the permitted period.
Perpetuity vs. perpetual trust. Modern dynasty trusts are designed to last for generations — in some jurisdictions, indefinitely — but are engineered so that interests vest within each generation, or are structured in states that have abolished or modified the RAP. A dynasty trust is not necessarily a perpetuity in the traditional sense, even if it functions perpetually in economic terms.
Core Elements
The traditional test for whether a future interest constitutes an unlawful perpetuity turns on three elements:
1. Remoteness of vesting. The interest must vest, if at all, within the perpetuity period. An interest that might not vest — or might vest outside the period under any possible chain of events, however improbable — is void under the traditional rule.
2. The perpetuity period. One or more lives in being at the time the interest is created, plus twenty-one years, plus any period of gestation for a child en ventre sa mère. The period is measured from the creation of the interest (at execution for an irrevocable instrument; at the testator's death for a will).
3. Indestructibility. Historical dictionaries, particularly Black's, emphasize that a key feature of a perpetuity is that the interest cannot be destroyed by the persons presently entitled to the property without the concurrence of the future taker — making it impossible for living persons to consolidate title and convey the property freely.
Why It Matters in Research
Perpetuity doctrine is one of the most technically demanding areas in property and trusts research, and the corpus presents several traps.
Temporal instability of the rule. The traditional common-law rule — often called the rule in Whitby v. Mitchell in its modern form and traced to the Duke of Norfolk's Case — was stable for centuries but has undergone radical legislative revision since the 1980s. Uniform laws (the Uniform Statutory Rule Against Perpetuities and later the Uniform Trust Code) introduced wait-and-see approaches and savings clauses. Many U.S. jurisdictions have since abolished or dramatically extended the perpetuity period for trusts. Historical sources in this corpus reflect the traditional rule; modern practice may differ sharply.
The "might" problem. The traditional rule is a rule of logical possibility, not actuarial probability. Researchers reading historical sources will encounter arguments that seem absurd by modern standards — the fertile octogenarian, the unborn widow — because the rule required courts to imagine any possible outcome, however unlikely. This makes historical case analysis in this area particularly treacherous.
Charitable trusts are exempt. The rule against perpetuities does not apply to interests vested in charity, or to gift-over from one charitable purpose to another. This exemption is consistent across historical sources but easy to overlook when reading older treatises.
Financial perpetuity calculations. When historical documents use perpetuity in the mathematical/financial sense (Webster's 1913 flags this: the number of years in which simple interest equals principal), the term has nothing to do with the RAP. Endowment valuations, annuity calculations in wills, and financial correspondence may use this sense without any implication of legal invalidity.
Corpus connections. Research into perpetuity doctrine connects naturally to the law of future interests (remainders, executory interests, reversions), trust duration law, powers of appointment, and modern dynasty trust planning. The RAP cannot be understood in isolation from the broader system of future interests it was designed to police.
Historical Dictionary Support
The historical dictionaries in this corpus show broad agreement on the core definition but reveal meaningful differences in emphasis and completeness.
Black's (both editions) offers the most technically precise definition, centering on the indestructibility element — the idea that the future limitation cannot be destroyed without the concurrence of the future taker. This is an important feature that distinguishes a true perpetuity from a merely remote interest.
Bouvier's adopts the Randall formulation emphasizing the commerce-removal rationale: any limitation taking property out of commerce beyond the permitted period. Bouvier's is also the most useful for tracking the scholarly debate over specific cases, citing Gray and Lewis on perpetuities and flagging contested authority directly.
Burrill's is notable for its layered approach: it defines perpetuity first in plain terms (indefinite inalienability), then distinguishes the condition of the estate from the limiting instrument — a structural distinction the other dictionaries collapse. Burrill's reference to Kent's Commentaries gives researchers a useful treatise anchor.
Anderson's adds a dimension the others underplay: the sovereign's "absolute immortality in his political capacity" as a distinct, non-property sense of perpetuity. This usage, largely archaic, appears in constitutional and public law materials and can confuse researchers reading older political theory embedded in legal texts.
Rapalje & Lawrence is the least useful entry for this term. The relevant passage is fragmentary and begins mid-sentence, reflecting a digitization artifact. Researchers should not rely on this source for perpetuity doctrine.
None of the historical dictionaries anticipates the modern legislative reforms that have substantially dismantled the rule in many jurisdictions. All reflect the traditional common-law rule as fixed law, which it no longer is for a significant portion of U.S. trust practice.
Jurisdictional Note
Jurisdictional variation in this area is extreme and materially affects research. Approximately half of U.S. states have abolished the Rule Against Perpetuities for trusts or extended the permissible period to 360 years or longer, enabling dynasty trust planning. Many others have enacted wait-and-see statutes or adopted USRAP savings provisions. The traditional common-law rule remains operative in some states. Researchers must identify the governing jurisdiction and applicable statute before applying any historical source to a modern question.
Encyclopedia Cross-Reference
Dynasty Trusts and Perpetual Trusts — Planning Beyond the Rule Against Perpetuities (The Law Mind Trusts, Estates & Probate Encyclopedia, estates_98)
Powers of Appointment and the Rule Against Perpetuities (The Law Mind Trusts, Estates & Probate Encyclopedia, estates_114)
Modern Reforms and Abolition of the Rule Against Perpetuities in Selected Jurisdictions (The Law Mind Trusts, Estates & Probate Encyclopedia, estates_112)