Definition
Post natus (Latin: "born after") is a term from private international law and early English common law designating a person born after a legally significant historical event — typically a political union, revolution, or change in sovereignty — whose rights, nationality, or legal status depend on the timing of that birth relative to the event.
The term carries two distinct but related applications:
1. SUCCESSION AND FAMILY LAW (historical): In older legal writing, post natus simply meant a second or younger son — one born after an elder sibling. Used in this sense, the term was a descriptor in inheritance and primogeniture contexts, distinguishing later-born children from the firstborn heir.
2. PRIVATE INTERNATIONAL LAW (constitutional and conflict of laws): The more jurisprudentially significant use designates persons born after a critical political event that altered the governing sovereign or legal order. The paradigm cases are:
- The Act of Union (1707), which merged England and Scotland. Persons born in Scotland after the Union were regarded as natural-born subjects of Great Britain, with different legal standing than those born before (the ante nati). This distinction generated one of the most debated questions in early English conflicts doctrine.
- The American Revolution. Following independence, questions arose whether persons born in the former colonies after the break with Britain retained rights as British subjects, or whether their status was entirely governed by the new American legal order. The post natus/ante natus distinction shaped early American nationality and property law.
In both contexts, the term functions as a temporal marker: birth after the triggering event is the fact that determines which legal system governs the person's status, rights of inheritance, and capacity to hold property.
---
Common Confusion
POST NATUS vs. ANTE NATUS: These terms are a matched pair and must be read together. Ante natus designates a person born before the relevant historical event. The legal consequences attached to each designation — particularly regarding allegiance, property-holding capacity, and subject status — were often directly opposed. Researchers who encounter one term in a source should immediately search for the other, as the doctrine only makes sense comparatively.
POST NATUS vs. NATUS POST LIMINIUM: Post liminium (or postliminy) is a distinct doctrine concerning the restoration of rights to persons or property recovered from enemy occupation. The "post" in post natus refers to birth timing relative to a political event; the "post" in post liminium refers to return across a legal boundary. The terms share Latin roots but address entirely different problems.
---
Why It Matters in Research
This term is almost exclusively a term of historical legal research. Modern nationality law has rendered the ante natus/post natus distinction largely obsolete as an operative legal category, but the doctrine generated significant early Anglo-American case law and treatise commentary, particularly on:
- Natural-born subject status under English common law
- Property-holding capacity of aliens and former colonists after the Revolution
- The reach of Calvin's Case (1608), the foundational English authority on subject status by birth, which post natus doctrine directly engages
Researchers working in early American constitutional history, conflict of laws, or English legal history will encounter this term in treatises from the 17th through 19th centuries. Blackstone discusses the ante natus/post natus distinction in the Commentaries in the context of natural-born subjects. American lawyers debated the status of loyalists and their property under these categories in the decades immediately following independence.
Trap for researchers: In older sources, post natus sometimes appears without context as merely "younger son" in a succession or primogeniture discussion, carrying no international law significance. The surrounding subject matter — inheritance disputes versus nationality or property-holding capacity — will clarify which meaning is operative.
The term does not appear in modern statutory codes or constitutional provisions as a defined term. Its research value is almost entirely confined to historical primary sources, early treatises, and conflict-of-laws scholarship examining the colonial and early republic periods.
---
Historical Dictionary Support
Both editions of Black's Law Dictionary carry virtually identical entries, treating the term as both a family law descriptor (younger son) and a private international law category. The entries are accurate but brief, and both use the same illustrative examples — the American Revolution and the Act of Union — without distinguishing which context generated the more doctrinally developed body of law.
What the historical dictionaries omit: Neither edition engages with Calvin's Case, which is the essential background authority for understanding why the post natus doctrine mattered. They also do not note that the post natus/ante natus distinction was the subject of serious analytical dispute among early American jurists, particularly regarding the property rights of loyalists. A researcher relying solely on these entries would understand what the term means but not why it generated controversy or where to find the primary authorities.
The consistency between the two editions suggests the entry was not revised between printings — a sign that the editors regarded the doctrine as settled historical material rather than evolving law.
---