Definition
A Latin term from Roman law meaning a formal request or petition. In its primary legal sense, postulatio referred to the first procedural step in a Roman criminal prosecution — the moment at which an accuser appeared before the praetor, declared an intention to bring criminal charges against a named person, and sought the magistrate's authority to proceed. It was the threshold act that opened the machinery of formal prosecution.
In old English ecclesiastical law, the term carried a secondary and distinct meaning: a species of petition by which a cathedral chapter or other ecclesiastical body requested the transfer of a bishop from one see to another, as distinguished from a full canonical election.
Common Confusion
The comparison to "swearing out a warrant" offered by Black's Law Dictionary is a useful orientation but should not be pressed too far. The postulatio did not by itself initiate a prosecution or authorize arrest; it was a request for permission to proceed, dependent on the praetor's acceptance. The procedural posture is closer to seeking leave of court than to the automatic warrant issuance familiar in modern common law systems.
Why It Matters in Research
Postulatio is a term of limited direct application in modern common law research but appears with some frequency in two distinct research contexts: Roman and civil law sources, and ecclesiastical law materials.
In civil law and Roman law research, postulatio marks the formal commencement of criminal proceedings — functionally analogous to what modern researchers would recognize as the initiation of a complaint or the swearing out of a warrant. Understanding this procedural position is essential when reading classical sources or civil law treatises that describe Roman criminal procedure in sequence. The term will appear in discussions of the praetor's role and the structure of the quaestiones perpetuae, the standing criminal courts of the late Roman Republic. Researchers working through comparative criminal procedure, or tracing the historical origins of prosecutorial discretion and the formal accusation requirement, should treat postulatio as a starting point in that analytical chain.
In ecclesiastical law research, the term's secondary meaning requires careful attention. The postulatio for a bishop's translation was procedurally distinct from electio (election) because it was used when canonical impediments — such as the bishop already holding another see — made ordinary election technically improper. The distinction between election and postulatio appears in canon law texts and in English ecclesiastical sources dealing with episcopal appointments, particularly in medieval and early modern materials. Researchers working in that area should not treat postulatio and electio as interchangeable.
The term does not survive into modern Anglo-American legal usage in either of its historical senses. It will not appear in modern statutory codes or contemporary case law. Its presence in a source is itself a marker of age or classical learning.
Historical Dictionary Support
Black's Law Dictionary (1st and 2nd editions) and Rapalje & Lawrence are in agreement on the essentials: postulatio is the first act in a Roman criminal proceeding, consisting of a request to the praetor to authorize prosecution. Black's provides the richer account in both editions, explaining that the accuser appeared personally before the praetor, named the intended defendant, and sought formal authority to proceed — a description that maps the term onto the structural logic of modern warrant practice, which is a useful but imperfect analogy. Black's both editions also include the ecclesiastical sense (petition for episcopal transfer), though the 2nd edition entry appears to have been truncated at that point in the available source text.
Rapalje & Lawrence is notably more spare, identifying postulatio only as the first act in a criminal proceeding under the civil law, with a cross-reference to Holtz's Encyclopedia rather than a substantive independent definition. This reflects the dictionary's general approach to civil law terms and means researchers relying solely on Rapalje & Lawrence will miss both the procedural detail and the ecclesiastical meaning entirely.
None of the historical dictionaries develop the ecclesiastical sense in depth. For that meaning, canonical and ecclesiastical law sources would be the appropriate next stop.
Jurisdictional Note
Postulatio is a term of Roman and civil law, with a secondary usage in English ecclesiastical law. It has no operative meaning in modern American or English common law jurisdictions. Research context determines which meaning is relevant.