Definition
A possibility on a possibility is a contingency so remote and speculative that the law will not recognize it as a valid basis for limiting a future interest. The concept describes a condition that can only be satisfied if two or more uncertain events each occur in sequence — so that the interest depends not merely on one open question, but on a further uncertainty stacked upon the first. Because the law of future interests historically demanded that contingencies be definable and not wholly speculative, an interest conditioned on a possibility resting upon another possibility was treated as void or invalid.
The classic illustration from Coke: if a remainder is limited to a living person's son named "John" or "Edward," the grant is bad if the person currently has no son of that name. The contingency is not merely that he will have a son (one possibility), but that he will have a son bearing a specific name (a second, independent uncertainty stacked on the first). The cumulative remoteness defeated the interest.
Common Confusion
POSSIBILITY ON A POSSIBILITY vs. MERE POSSIBILITY: A single contingency — a "mere possibility" — was disfavored but could be valid depending on context and the type of future interest involved. A possibility on a possibility was treated as categorically too remote, a distinct and more severe defect. Researchers should not conflate the two: historical sources use "mere possibility" to caution against certain contingent remainders, but "possibility on a possibility" signals an absolute bar to validity, not just a warning.
POSSIBILITY ON A POSSIBILITY vs. RULE AGAINST PERPETUITIES: The two doctrines address related but distinct problems. The Rule Against Perpetuities polices interests that might vest too far in the future. The possibility on a possibility doctrine addresses interests that are contingent on conditions so speculative they are legally meaningless — the defect is qualitative remoteness, not temporal remoteness. The two rules could condemn the same interest, but for different reasons.
Why It Matters in Research
This term is primarily encountered in older English common law materials and in American property law treatises and cases from the eighteenth and nineteenth centuries dealing with contingent remainders. Modern property scholarship has largely absorbed the concern behind this doctrine into the Rule Against Perpetuities and related rules on vesting, which means the phrase itself appears infrequently in twentieth-century sources. Researchers analyzing historical deeds, wills, or remainder instruments from the colonial or early republic period may encounter "possibility on a possibility" as an explicit basis for invalidating a future interest and should recognize it as a distinct common law rule, not a precursor to or synonym for the Rule Against Perpetuities.
The doctrine reflects the classical common law hostility to contingent remainders generally. Under strict common law doctrine, contingent remainders were disfavored, and courts looked for reasons to destroy or void them. A remainder dependent on stacked contingencies gave courts clear analytical grounds for invalidation. As American jurisdictions abolished or relaxed the destructibility of contingent remainders — and as the Rule Against Perpetuities became the dominant framework for policing speculative future interests — the freestanding "possibility on a possibility" doctrine receded from practical use, but its logic persists in how courts and treatise writers explain why certain speculative remainders failed under older law.
Researchers should also be alert to the fact that modern secondary sources may discuss this concept without using the phrase, describing the problem instead in terms of vesting requirements or the perpetuities analysis. Cross-referencing entries on contingent remainders, executory interests, and the Rule Against Perpetuities will usually be necessary to reconstruct the full doctrinal picture around any historical instrument where this issue arises.
Historical Dictionary Support
Black's Law Dictionary supplies the essential definition and traces the rule to Coke (2 Coke, 51), grounding it firmly in early common law authority. The entry is brief but precise: the defect is the stacking of contingencies such that fulfillment requires not one uncertain event but a further uncertainty dependent on the first. Black's example — the son of a specific name — is drawn directly from Coke and captures the doctrine's logic efficiently.
Historical dictionaries do not fully develop the relationship between this rule and the broader doctrinal context of contingent remainders or the Rule Against Perpetuities, leaving modern researchers to supply those connections. The Coke citation is genuine and important; Coke's treatment of contingent remainders in his commentary on Littleton was authoritative for centuries and should be consulted for any deep historical analysis. Subsequent treatise writers, including Blackstone and Kent, addressed contingent remainders at length, though not always using this precise phrase.
Encyclopedia Cross-Reference
Future Interests — Reversion, Possibility of Reverter, Right of Entry (The Law Mind Property Law Encyclopedia)