Definition
In posse (Latin: "in possibility") describes something that exists in potential only — not yet in actual being, but capable of coming into existence. It is the condition of a thing or person that may exist, or a right, interest, or status that may arise, but which has not yet materialized into fact.
The term functions as a modifier applied to future or contingent legal interests. An unborn child, for example, is said to be in posse — the child may exist at some future point, but has no present legal existence. Similarly, a right or estate that depends on a future event exists in posse until that event occurs and brings it into actual being.
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Common Language
Modern common usage (Wiktionary): "In possibility, having a potential to exist, in potential but not in actuality (contradistinguished by in esse)."
Historical common usage (Webster's 1913): "In possibility; possible, although not yet in existence or come to pass — contradistinguished from in esse."
Editorial note: The common and legal meanings here are unusually well aligned — both treat in posse as a Latin phrase describing potential rather than actual existence. The legal usage, however, carries technical weight when applied to property interests, rights, and legal personhood, where the distinction between potential and actual existence determines enforceable legal consequences. In ordinary speech the phrase is rare and, when used, typically borrowed from legal or philosophical contexts.
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Common Confusion
In posse is consistently paired against in esse, which describes something in actual, present existence. The confusion risk is not between two different terms used interchangeably but rather in misreading sources that use one without making the contrast explicit. In older legal writing, an author may describe a right or person as existing only in posse without restating the in esse contrast, and researchers unfamiliar with the pair may misread the passage as simply describing a weak or qualified right rather than one with no present legal existence at all. The distinction is binary: in esse or in posse — there is no intermediate category in the classical framework.
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Why It Matters in Research
This term appears most frequently in three research contexts: (1) property law, particularly future interests and contingent remainders, where the vesting of an interest depends on whether it has moved from in posse to in esse; (2) the legal status of unborn persons, where rights and protections hinge on whether a child is in esse or in posse at the relevant moment; and (3) older pleading treatises and equity texts, where courts assessed whether parties or interests were sufficiently in existence to be brought before the court.
Researchers working in pre-twentieth-century materials will encounter in posse frequently in discussions of contingent remainders, executory interests, and the Rule Against Perpetuities. The term itself rarely shifts in meaning across historical sources — its stability is one of its notable features — but the legal doctrines it modifies have evolved considerably. What a contingent remainder in posse meant under common law pleading differs from how modern courts might characterize a future interest.
The encyclopedia cross-reference to the Posse Comitatus Act is a false cognate trap worth flagging explicitly: posse comitatus derives from a different Latin construction (power of the county) and shares no conceptual relationship with in posse. Researchers who arrive at in posse through a posse comitatus search context should redirect immediately.
Burrill's citation to Townshend on Pleading (Pl. 142) is the most specific historical anchor for the term in a pleading context and is worth locating if researching how courts historically handled parties or interests that were asserted to exist only in possibility.
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Historical Dictionary Support
The historical dictionaries are in complete agreement on this term. Black's (both editions) and Burrill define in posse identically: "in possibility; not in actual existence," with each directing the reader to in esse as the contrasting concept. This consistency across sources spanning different periods of publication reflects the term's Latin roots and its resistance to doctrinal drift — it is a logical and grammatical pair, not a term whose content was shaped by common law development.
Burrill adds the most context, appending a separate maxim — "In quo quis delinquit, in eo de jure est puniendus" — after the in posse entry, but this appears to be a placement artifact of the dictionary's organization rather than a substantive connection. Researchers should not read a criminal law dimension into in posse based on that proximity.
What the historical dictionaries do not address is the practical doctrinal work the term performs — particularly in the law of future interests and the rules governing who may hold or assert rights. That gap means historical dictionary entries alone are insufficient; researchers should consult treatises on property and equity for the term in operation.
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Encyclopedia Cross-Reference
The encyclopedia entry for Posse Comitatus Act (The Law Mind Military, Veterans & Admiralty Law Encyclopedia) shares the word posse but is not conceptually related to in posse. No Law Mind Encyclopedia entry directly addresses in posse as a substantive topic; the term is best pursued through encyclopedia entries on future interests, contingent remainders, and legal personhood.
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