Handbook of the History of Logic: - Fordham University Faculty

Developments in the Fifteenth and Sixteenth Centuries 641
tain and rhetoric, freer. 154 As he had remarked earlier, a good dialectical proof
could not be otherwise, but a rhetorical proof can always be put another way. 155
In the section on Topics, however, he takes up the notion of signs, which he divides
into necessary and probable. 156 He also uses an explicit probability operator, placing
‘probabile est igitur’ in front of the conclusion of an argument from probable
signs.He then links the discussion of signs with the personal Topics, saying that
they are both less relevant to the dialectician, who needs necessary and evident
arguments, than to the rhetorician, but their discussion should not be left to the
rhetorician. Arguments using premisses based on signs or the personal Topics need
to be put into the form of syllogisms, enthymemes, induction or example. For instance,
he gives the argument: “It is unlikely (verisimile non est) that students of
literature should indulge in pleasures, Coelius is a student of literature, therefore
it is unlikely that he indulges in pleasures.” The example suggests that he wanted
to treat probability operators as part of a deductive system, rather than using
them to construct a non-deductive probabilistic logic.
In the Erotemata Dialectices, enthymeme is linked with signs, and Melanchthon
explains that Aristotle defined enthymeme as an imperfect syllogism whose premisses
are probabilities (ex icotibus) and signs. 157 However, the point of discussing
true-seeming (verisimilia) signs is only to warn us against misleading and fallacious
arguments. In the section on Topics, signs are now discussed quite separately
from the personal Topics, and are divided into those that are necessary and those
that are “not necessary but are associated accidents”, called ‘eikota’. 158 We have
to be very careful using arguments based on the latter, lest we deceive ourselves,
as often happens “in suspicionibus et aliis malis persuasionibus.” We should remind
ourselves here that suspicio and persuasion belong to rhetoric. All in all,
Melanchthon, despite clear humanist interests, does not write like a logician who
is intent on legitimatizing informal, probabilistic argumentation.
Agostino Nifo firmly relegates one kind of enthymeme to rhetoric. In his Dialectica
ludicra, he quotes Michael Psellus, an eleventh-century Byzantine writer,
whose work on rhetoric divided consequences into necessary and contingent. 159
The latter were those that merely persuade without proving or convincing, such
as rhetorical enthymeme and example. Nifo went on to claim that there are two
sorts of enthymeme, the analytical enthymeme which differs from a syllogism only
in that it uses one premiss, and the rhetorical enthymeme, which differs from a
syllogism both in its use of just one premiss and in the fact that the suppressed
premiss is neither necessary nor probable but merely true-seeming (verisimilis). 160
Such a premiss is not dependent on opinion or fact, but on a link with action. 161
154 Melanchthon, Compendiaria Dialectices Ratio, col. 743.
155 Melanchthon, Compendiaria Dialectices Ratio, col. 733.
156 Melanchthon, Compendiaria Dialectices Ratio, cols. 750–751.
157 Melanchthon, Erotemata Dialectices, cols. 617–619.
158 Melanchthon, Erotemata Dialectices, cols. 704–706.
159 Niphus, Dialectica ludicra, f. 110 va.
160 Niphus, Dialectica ludicra, f. 110 vb–111 ra.
161 Niphus, Dialectica ludicra, f. 111 ra: “assumptio verisimilis non accipitur ab opinionem: vel