Definition
In Roman and civil law, the father of one's father-in-law — that is, the paternal grandfather of one's spouse. The term belongs to the specialized vocabulary of Roman affinal kinship, which assigned distinct Latin designations to each degree and line of relationship by marriage. PROSOCER identifies a specific ascendant in the wife's paternal line, one generation above the SOCER (father-in-law).
Why It Matters in Research
PROSOCER is a term of civil law taxonomy, not a term of art in common law systems. Researchers will encounter it almost exclusively in two contexts: (1) texts and commentaries drawn from Roman law sources, including Justinian's Digest and Institutes, and works of civilian jurists cited in common law treatises by way of comparison; and (2) historical legal dictionaries and glossaries compiled during the period when Roman law terminology was still considered necessary reference material for trained lawyers.
The practical significance of this vocabulary in operative legal texts is narrow. Roman law developed intricate rules governing marriage prohibitions, intestate succession, and degrees of affinity, and the precise Latin kinship terms served as the technical shorthand for those rules. When reading a civil law source that restricts marriage or inheritance rights based on degrees of affinity, knowing that PROSOCER identifies a specific degree in the wife's ascending paternal line matters for correctly parsing the rule. In common law sources, the term appears almost never in operative legal text — its presence signals that the author is drawing on Roman or civilian authority for comparative or historical purposes.
Researchers working in Louisiana, Quebec, or other mixed jurisdictions with a civilian heritage may occasionally encounter affinal kinship terminology in older statutory or doctrinal sources. Elsewhere in U.S. or English law, encountering PROSOCER is a reliable signal that the text is engaged in comparative or historical scholarship rather than stating binding doctrine.
There is no meaningful evolution of this term's legal meaning over time — its usage remained stable and confined to civil law commentary throughout its documented history. The research trap is not definitional drift but rather the assumption that precision in Roman kinship nomenclature maps onto common law categories. Common law sources use broader and less granular language for affinal relations, and a Roman law rule stated in terms of PROSOCER has no direct common law equivalent to retrieve.
Historical Dictionary Support
All four sources — Black's (both editions), Rapalje & Lawrence, and Burrill — are in complete agreement: PROSOCER means a father-in-law's father, or equivalently, the grandfather of one's wife. The definitions are nearly verbatim across sources, reflecting that each is drawing from the same narrow civilian tradition rather than from independent lines of authority.
Burrill alone cites a source: "Calv. Lex." — a reference to Johannes Calvinus's Lexicon Juridicum Juris Caesarei Simul et Canonici, a standard civil law lexicon of the early modern period. This citation is the closest any of the four sources comes to grounding the term in primary authority, and it confirms the term's origin in the scholarly apparatus of Roman and canon law rather than in adjudicated common law.
None of the historical dictionaries expands on the operative legal significance of the term — they supply the gloss and no more. This is characteristic of how common law dictionaries handled Roman kinship vocabulary: treat it as a translation problem, not a doctrinal one. Researchers seeking the legal rules to which PROSOCER was relevant must turn to civil law sources directly.
Jurisdictional Note
PROSOCER is a term of Roman and civil law with no recognized independent status in common law jurisdictions. In civilian or mixed jurisdictions, it may appear in historical materials relating to affinity-based marriage prohibitions or succession rules, but modern codifications in those systems use vernacular terminology rather than classical Latin kinship labels.