Handbook of the History of Logic: - Fordham University Faculty

640 E. Jennifer Ashworth
be either necessary or probable. 148 “A man is an animal, therefore every man
is an animal” is necessary, given that any man is necessarily an animal, but “A
mother loves her child, therefore this mother loves her child” is probable in the
sense that there is no necessary link between antecedent and conclusion. The
conclusion follows often, but not always. We have here a recognition of genuine
informal arguments, but it is not enlarged on. It is presumably based either on
Boethius’s De topicis differentiis where Boethius speaks of arguments which are
“readily believable and not necessary”, such as “If she is a mother, she loves [her]
child”, 149 or on Cicero, De inventione I.29.46.
Fonseca also has a few relevant remarks in his discussion of the Topic from
associated accidents. 150 These are circumstances which are often not necessarily
connected, and which give rise to suspicio, that epistemic state associated with
rhetoric. However, Fonseca explicitly allows that the dialectician may not only
teach the invention of such arguments, but use them insofar as they give rise to
probabilities. Toletus too had some relevant material in his discussion of the Topic
from associated accidents. 151 He noted that there are two modes of argument,
necessary and non-necessary. “It is bearing fruit, therefore it has flowered” is
necessary, but “People are drinking, therefore there will be fights” (Bacchanalia
sunt, ergo rixae erunt) is non-necessary. The latter mode is related to other
arguments based on natural signs, physiognomy, prodigies, portents, and those
once based on auguries but now empty and fallacious. He suggests that they are
based on suspicio, and they are not, or not all, necessary or probable. In effect,
this once more relegates such arguments to rhetoric rather than logic.
Other discussions found in the logical literature relate to the classification of enthymemes.
Aristotle had written (Prior Analytics 70a10–11) that “An enthymeme
is a deduction starting from probabilities or signs [. . .]”, where these are two types
of proposition, and the same distinction between probabilities or non-necessary
signs and necessary signs was found in Quintilian. 152 Commenting on Aristotle’s
classification, Clichtoveus writes that the first type of proposition is contingent,
for instance, “A mother loves her children”, and that it gives rise to a dialectical
enthymeme, such as: “A mother loves her children, therefore a mother does not
hate her children.” 153 His example, however, seems more like a non-formal valid
deductive argument than it does a genuinely probabilistic informal argument.
In the section on enthymeme found in the Compendiaria Dialectices Ratio,
Melanchthon emphasizes that rhetoricians and dialecticians use the same ratio
argumentandi and the same structure of arguments, though dialectic is more cer-
148 Fonseca, Instituições Dialécticas, p. 340.
149 Stump, Boethius’s De topicis differentiis, p. 40.
150 Fonseca, Instituições Dialécticas, p. 542–544. He uses the title ‘De locis praecurrentium,
comitantium et subsequentium’, but tells the reader that this is what Cicero called the Topic
from adjuncts. In turn, that Topic is the one also known as the Topic from associated accidents
(De communiter accidentibus).
151 Toletus, Introductio in dialecticam, f.82b.
152 Quintilian, Institutio oratoria, V.9.1–8.
153 Clichtoveus, Introductiones artificiales (Parisiis, 1517), f. 100 r–v.