Handbook of the History of Logic: - Fordham University Faculty

Developments in the Fifteenth and Sixteenth Centuries 633
and Aristotle twice defines the syllogism as a discourse (oratio) in which, certain
things being stated, something other than what is stated follows of necessity from
their being so. (Prior Analytics 24b18–20; Topics 100a 25–26). It is quite possible
that the Greek word was intended to be taken in two senses, with the Prior
Analytics dealing with syllogisms in the technical sense of arguments with two
premisses and three terms arranged so arranged that each term appears twice, the
middle term in both premisses, and each of the other terms in just one premiss
and the conclusion, and the Topics dealing with deduction in general. However,
the standard medieval and post-medieval assumption was that the technical sense
of syllogism is intended in each case. 120 Accordingly, the Topics (100a25–101b24)
was taken to list four species of syllogism, demonstrative, dialectical, deceitful
(the syllogismus falsigraphus or pseudographus, which argues from falsehoods belonging
to the special sciences), and sophistical or contentious (litigiosus). We
will not be concerned with the last two, which are both fallacious. In the Topics
(105a10–19) Aristotle also tells us that there are two species of dialectical reasoning
(dialecticarum ratiocinationum), syllogismus and inductio. FromhisRhetoric
we learn that rhetoric accompanies dialectic (Rhetorica assecutiva dialecticae est),
that it is concerned with persuasion, and that it uses two other types of reasoning,
enthymeme, which is the rhetorical syllogism, and example, which is the rhetorical
induction (Rhet. 1355a4–8, 1356a36–b12). These four types of reasoning
(argumentatio) were neatly summarized by Peter of Spain, 121 and they formed a
standard list to be included in logic texts, despite the association of enthymeme
and example with rhetoric.
Other standard material was drawn from Boethius’s two works on the Topics,
In Ciceronis Topica and De topicis differentiis. He discussed the uses of the
words ‘logica’ and ‘dialectica’; following Cicero, he described logic as a system of
discourse (ratio disserendi); 122 and he told his readers that an argument “is a
reason that produces belief regarding something that was in doubt”. 123 Moreover,
he handed on the important distinction between invention (the finding of material
for arguments) and judgement. 124
If we now ask what counts as dialectic and whether it differs from logic, two
main answers are possible. One can regard ‘logic’ and ‘dialectic’ as merely two
names for one discipline, or one can regard dialectic as a sub-part of logic which
studies dialectical syllogisms as presented in Aristotle’s Topics. Both of these answers
were generally recognized as acceptable in the medieval and post-medieval
period, and one did not exclude the other. A third answer, based on the discussion
of dialectical invention by Rudolph Agricola, is that dialectic focusses not on
the dialectical syllogism but on Topical discourse and debate, and hence, accord-
120Note that the ‘technical’ sense was normally extended to embrace hypothetical and expository
syllogisms.
121Peter of Spain, Tractatus, p. 56.
122Stump, Boethius’s De topicis differentiis, p. 29.
123Stump, Boethius’s In Ciceronis Topica, p. 29; Stump, Boethius’s De topicis differentiis, p.
39 (“Argumentum est ratio rei dubiae faciens fidem”.)
124Stump, Boethius’s In Ciceronis Topica, p. 25.