Definition
A rhetorical figure in which arguments are assembled from multiple points of view and then converged upon a single conclusion. In legal usage, diallage describes a mode of argumentation — particularly in advocacy and pleading — where counsel marshals varied lines of reasoning, each approaching the question differently, and directs them collectively toward one dispositive point. The technique is cumulative and convergent: the force of the argument derives not from any single premise but from the weight of multiple perspectives arriving at the same destination.
Common Language
Modern common usage (Wiktionary): "A figure of speech in which multiple arguments are brought to bear on a single point." Also listed as a mineralogical term for a green form of pyroxene.
Historical common usage (Webster's 1913): "A figure by which arguments are placed in various points of view, and then turned to one point."
The common and legal meanings here are essentially identical — diallage entered legal dictionaries directly from classical rhetoric without modification. The mineralogical sense (a variety of pyroxene) is entirely unrelated and creates no meaningful confusion in legal sources.
Why It Matters in Research
Diallage is a term a researcher is far more likely to encounter than to search for. It appears in older treatises on rhetoric and logic as applied to law — particularly in works on advocacy, pleading, and argumentation from the eighteenth and nineteenth centuries — but it was never a term of art with operative legal consequences. No cause of action, no procedural rule, and no evidentiary standard turns on diallage.
Its presence in Black's and Rapalje & Lawrence signals something important about how early American legal dictionaries were constructed: they drew heavily on classical rhetoric and encyclopedic sources (the repeated citation to "Enc. Lond." — the Encyclopaedia Londinensis — is the tell). Researchers working in nineteenth-century advocacy literature, legal education materials, or the history of legal rhetoric may encounter the term as descriptive of argumentative method.
The Rapalje & Lawrence entry is notable for an artifact of typesetting or compilation error: the diallage definition runs directly into a reference to the Dialogus de Scaccario, a medieval English fiscal treatise. This is not a related concept — it is a formatting collision in the source dictionary. Researchers using digitized versions of Rapalje & Lawrence should be alert to this kind of run-on text, which can confuse keyword searches and automated parsing.
Historical Dictionary Support
All three source dictionaries reproduce functionally identical definitions, each tracing to the Encyclopaedia Londinensis rather than to any legal authority. This uniformity reveals that diallage was carried forward through dictionary succession — Black's 2nd edition repeating Black's 1st, which drew from Rapalje & Lawrence or a common encyclopedic source — rather than developing through legal usage or judicial treatment. No source offers a legal example, case application, or statutory context. Webster's 1913 matches the legal definition closely, confirming the term migrated from rhetoric into law dictionaries intact and without transformation. The historical sources agree completely, but their agreement reflects shared derivation from a single rhetorical source rather than independent legal development.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Rhetoric and Legal Argumentation; History of Legal Dictionaries.