topical logic

{{Short description|Reasoning from commonplace topoi}}

Topical logic is the logic of topical argument, a branch of rhetoric developed in the Late Antique period from earlier works, such as Aristotle's Topics and Cicero's Topica. It consists of heuristics for developing arguments, which are in the first place plausible rather than rigorous, from commonplaces (topoi or loci). In other words, therefore, it consists of standardized ways of thinking up debating techniques from existing, thought-through positions. The actual practice of topical argument was much developed by Roman lawyers.{{Cite book|chapter-url=http://plato.stanford.edu/entries/boethius/|title = The Stanford Encyclopedia of Philosophy|chapter = Anicius Manlius Severinus Boethius|year = 2021|publisher = Metaphysics Research Lab, Stanford University}}{{Cite book|chapter-url=http://plato.stanford.edu/entries/logic-ancient/|title=The Stanford Encyclopedia of Philosophy|chapter=Ancient Logic|year=2020|publisher=Metaphysics Research Lab, Stanford University}} Cicero took the theory of Aristotle to be an aspect of rhetoric.A. A. Long, From Epicurus to Epictetus: Studies in Hellenistic and Roman Philosophy (2006), p. 302. As such it belongs to inventio in the classic fivefold division of rhetoric.

The standard classical work on topical logic was the De Topicis Differentiis (On Topical Differentiae) by Boethius. Differentiae refer to case analysis, being the differentiations used to distinguish the cases into which a question is divided. Besides Aristotle and Cicero, Boethius built on Themistius.George Alexander Kennedy, Classical Rhetoric & Its Christian & Secular Tradition from Ancient to Modern Times (1999), p. 202. In terminology, the Greek axioma and topos in Boethius became the Latin maxima propositio (maxim, universal truth) and locus.

In the Middle Ages topical logic became a theory of inference, for which the name "axiomatic topics" has been suggested.Norman Kretzmann, Anthony Kenny, Jan Pinborg, The Cambridge History of Later Medieval Philosophy: From the Rediscovery of Aristotle to the Disintegration of Scholasticism, 1100-1600 (1988), pp. 111-2. Abelard wanted to complete a theory of entailment by invoking the loci in Boethius to fill in conditionals, a flawed if bold development.{{Cite book|chapter-url=http://plato.stanford.edu/entries/abelard/|title=The Stanford Encyclopedia of Philosophy|chapter=Peter Abelard|year=2018|publisher=Metaphysics Research Lab, Stanford University}}Christopher J. Martin, Logic, pp. 172-3 in Jeffrey E. Brower, Kevin Guilfoy (editors), The Cambridge Companion to Abelard (2004). Peter of Spain, in his De locis, developed the ideas of Boethius.{{Cite book|chapter-url=http://plato.stanford.edu/entries/peter-spain/|title = The Stanford Encyclopedia of Philosophy|chapter = Peter of Spain|year = 2019|publisher = Metaphysics Research Lab, Stanford University}}

The De inventione dialectica of Rodolphus Agricola (1479) made large claims for this method, as an aspect of dialectic (traditionally contrasted with rhetoric) subordinated to inventio.Thomas M. Conley, Rhetoric in the European Tradition (1994), pp. 125-6. The precise relationship of "dialectic" and "rhetoric" remained vexed well into the sixteenth century, hinging on the role assigned to loci. It was expounded in different fashions by Philipp Melanchthon and Petrus Ramus.Harold J. Berman, Law and Revolution, II: The Impact of the Protestant Reformations on the Western Legal Tradition (2006), p. 112. The debate fed into the later development of Ramism.