Handbook of the History of Logic: - Fordham University Faculty

314 Henrik Lagerlund
way that one later finds in the thirteenth century textbooks on logic. The division
between the linguistic and non-linquistic fallacies is expressed and also the number
of fallacies are settled, that is, six linguistic and seven non-linguistic (see below
for a discussion about some of these).
The Sophistici Elenchi has been the inspiration of much original work in logic.
For example, a section of Aristotle’s work was throughout the Middle Ages very
important for discussing so called insolubles or paradoxes. One of the most famous
insoluble is the Liar-paradox: ‘This proposition is false’. In Sophistici Elenchi 25
(180a27-b7), Aristotle discusses the fallacy of confusing things said “in a certain
respect” (secundum quid) and things said ‘simply’ or ‘absolutely’ (simpliciter).
Aristotle discusses an example of a man that takes an oath to become an oathbreaker
and then breaks his oath. Such a man is on the whole or simply an
oath breaker, but in the particular case he is in a certain respect an oath-keeper.
Having said this Aristotle adds that “the argument is similar too concerning the
same man’s lying and speaking the truth at the same time”. This was taken as a
reference to the Liar-paradox and hence it was seen at least in the beginning of the
thirteenth century as an instance of the fallacy of secundum quid et simpliciter.
All early attempts to solve the Liar-paradox in this way were completely mistaken
and it was soon realised that Aristotle’s discussion was really about something
else. Perhaps this is the reason the textbook authors dealt with below did not at
all treat insolubles. 77
Disputing so-called de sophismatibus or sophisms was a standard part of midthirteenth
century logic teaching. An example of a sophistical proposition that
was disputed is ‘Every human being in necessarily an animal’. This is an example
of an ambiguous proposition, which is true or false depending on the interpretation
given to it. It is for example false when no humans exist, but if there are humans
it is true. Some dealt with such propositions by simply outlining under which
conditions they are true, while others felt that a proposition like this one must
always be true. Kilwardby, for example, argued that one can truly say that ‘Every
human being is necessarily an animal’ even when there are no humas, because the
species or intelligible form of human still remains and it is that which the utterance
‘human being’ signifies. 78
5 TREATISES ON LOGIC
5.1 The Tractates and Summaries
Special textbooks on logic began to be widely used already in the early twelfth
century. 79 Garlandus Compotista’s (d. early twelfth century) Dialectica and
Abelard’s Dialectica are two of the more famous ones. Towards the end of the
77 See [Spade, 1973] for a history of the Insolubilia-literature, and see [Spade, 2005] for a clear
exposition of the medieval discussion in general.
78 See [Lewry, 1981, 382].
79 See [de Rijk, 1967, I, Chapter 3].