In law school, few concepts elicit more confusion and groans than the Rule Against Perpetuities (RAP)—a notoriously complex doctrine in property law. Among the many hypotheticals used to teach the RAP, none is more famous (or infamous) than the “Fertile Octogenarian.” This fictional scenario pushes the boundaries of logic and biology to illustrate the technical precision of the rule.

What Is the Rule Against Perpetuities?

The Rule Against Perpetuities is a common law doctrine designed to prevent property interests from being tied up indefinitely. Its traditional statement is:

“No interest is good unless it must vest, if at all, not later than 21 years after some life in being at the creation of the interest.”

In simpler terms, future property interests must become legally enforceable (vest) within a certain time frame—specifically, within 21 years of the death of someone who was alive when the interest was created.

The Fertile Octogenarian Hypothetical

The "Fertile Octogenarian" is a thought experiment used to challenge students' understanding of the RAP. It assumes the following:

Suppose a grantor conveys property “to A for life, then to A’s children who reach the age of 30.” A is 80 years old and has living children.

While it might seem absurd to think that A could have more children at age 80, the common law requires us to assume that any living person is capable of having children—regardless of age or gender. This includes women well beyond childbearing years and even men in poor health. This assumption is known as the "presumption of fertility."

So, under the RAP, the grant to “A’s children who reach 30” is void because A could, theoretically, have another child tomorrow who might not reach age 30 within 21 years of A’s death. That possibility—no matter how remote—violates the rule.

Why It Matters

Although the Fertile Octogenarian is an unrealistic scenario, it serves an important purpose:

• Illustrates the Strictness of the RAP: The doctrine isn’t about what is likely to happen, but what could happen. Even a 0.01% chance that a future interest might vest too late renders it void.

• Demonstrates Legal Formalism: The hypothetical shows how the law sometimes values certainty and predictability over practical reality. Legal rules often use rigid tests to avoid subjective judgments.

• Encourages Careful Drafting: Real estate attorneys and estate planners must draft future interests with precision to avoid triggering the RAP. The scenario highlights the importance of using savings clauses, age limits, or alternative planning tools like trusts.

The Legacy of the Fertile Octogenarian

While many jurisdictions have abolished or modified the common law RAP through statutes like the Uniform Statutory Rule Against Perpetuities (USRAP), the Fertile Octogenarian remains a memorable rite of passage in legal education. It’s not just a bizarre legal fiction—it’s a vivid teaching tool that helps students internalize one of the most technical and foundational doctrines in property law.

And for that reason, the Fertile Octogenarian continues to live on—in lectures, casebooks, and bar exam prep courses—reminding us that in law, even the improbable must be planned for.

Know the Laws with LegalFix

Whether you want to understand what Rule Against Perpetuities (RAP) means or are looking for more information on how our legal system works, LegalFix is your go-to source for free legal information. You can find helpful articles and use the free search and information tools to better understand the state and federal laws that affect you. Just visit LegalFix.com to find all this content — and check back often for more valuable legal products and services coming soon.