Handbook of the History of Logic: - Fordham University Faculty

638 E. Jennifer Ashworth
the hands of Philip Melanchthon there was no real reduction, but instead a listing
of the so-called personal Topics, such as nation, age, education and sex, within
dialectic itself. 141 With respect to dispositio, Agricola discussed the problem of
presenting and organizing complete arguments and narrations, whether written or
spoken, at great length. In Melanchthon we find the same interest in dispositio. A
few remarks on order in the Compendiaria Dialectices Ratio grew into a full section
on logical method as a way of ordering discourse in the Erotemata Dialectices. 142
In turn we find method discussed in the second part of Ramus’s Dialectica, but
as we can see from his references to Agricola and Melanchthon, it is a mistake to
think that this was Ramus’s innovation. Sections on method became a standard
component of logic textbooks, and particularly after the publication of Zabarella’s
Opera logica, it became customary to add remarks on scientific method as well, in
a mixture of subject-matters that was not always happy. 143
To conclude, if we mean by the rhetoricizing of logic that material from the
rhetoricians came to be included in logic texts, this is certainly the case. How far
the material absorbed included informal persuasive devices is another matter.
4 INFORMAL ARGUMENTATION
Whether or not sixteenth-century logic leaves room for the notion of informal
arguments depends on how ‘formal’ and ‘informal’ are to be defined. The first
thing we need to understand is that logic was never formal in the modern sense.
There was no notion of an uninterpreted system with its own set of properties,
nor was there any notion of a formal interpretation such that, for instance, any
proposition just says T or F. While letters such as ‘a’ and ‘b’ could be used to
stand for propositions, and rules could be described in neutral language, the basic
assumption was always that logic served the purpose of finding and expressing
truths. That being said, one might make a distinction between formal and informal
arguments in terms of deductive validity, so that an informal argument is one
that is acceptable but not deductively valid. This still leaves various possibilities
open, with respect to both categories. In the case of valid deductive arguments,
we need a further distinction between formal and non-formal arguments. Some
arguments are such that their conclusion is true whenever the premisses are true,
no matter what non-logical terms are substituted. Other arguments are such
that their conclusion is true whenever the premisses are true just because of the
between rhetorical and dialectical Topics: see Stump, Boethius’s De topicis differentiis, pp.
79–95.
141 Melanchthon, Compendiaria Dialectices Ratio, cols. 751–755; Erotemata Dialectices, cols.
659–662.
142 Melanchthon, Compendiaria Dialectices Ratio, cols. 724–726; Erotemata Dialectices, cols.
573–578.
143 For more on discussions of method, see Cesare Vasoli, “The Renaissance concept of philosophy”
in The Cambridge History of Renaissance Philosophy, pp. 71–72; Jardine, “Humanistic
logic”, pp. 191–192; Ashworth, introduction to Sanderson, Logicae Artis Compendium, pp.
XLVIII–L.