Definition
In the civil law of evidence, conjectio is the process of grouping facts together and drawing an inference from them. The term describes both the act of assembling circumstantial indicators and the presumption that results. It is the evidentiary mechanism by which a conclusion is reached not from direct proof but from the collective weight of gathered circumstances pointing toward a particular inference.
Why It Matters in Research
Conjectio is a narrow, technical term from the Roman civil law tradition and appears primarily in treatises and historical legal texts rather than in common law case reporters. Researchers encountering the term in pre-modern legal literature should understand it as a precursor concept to the modern doctrine of presumption and circumstantial evidence reasoning — not a separate doctrine with ongoing independent application.
The term surfaces in civil law scholarship and in treatises that draw on Roman and continental European sources. When tracing the intellectual lineage of presumption doctrine in American or English law, conjectio may appear as a cited antecedent in works that synthesize civil and common law traditions. Burrill's citation to Matthaeus de Probationibus (Matthaeus, De Prob. c. 1, n. 43) signals that the primary scholarly elaboration lives in continental European treatise literature, not in common law reporters. Researchers working in that lineage should seek Matthaeus and similar civilians rather than expecting to find conjectio litigated as a term of art in English or American courts.
The concept is functionally absorbed in Anglo-American law by the overlapping vocabulary of presumption, inference, and circumstantial evidence. A researcher who finds conjectio in an early American treatise citation should treat it as a civil law gloss on what the common law would call presumptive reasoning rather than as an independent evidentiary rule requiring separate analysis.
Historical Dictionary Support
The historical dictionaries are in close agreement. Black's (both editions), Rapalje & Lawrence, and Burrill all define conjectio as a "throwing together" — a grouping of facts from which a presumption is deduced. The definitions are nearly verbatim across sources, suggesting the term's meaning was stable and uncontested in legal scholarship by the time these dictionaries were compiled.
Burrill alone provides a treatise citation (Matthaeus de Probationibus), which is characteristic of Burrill's more scholarly apparatus relative to the other dictionaries. That citation is the most useful pointer for researchers who need to trace the concept to its doctrinal roots. None of the historical sources attempt to import conjectio into common law doctrine as a functioning term; they record it as a civil law entry without elaborating its procedural application or comparing it to common law equivalents. This restraint is itself informative: the compilers treated it as a matter of definitional record, not as a term requiring advocacy or synthesis.