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sentence there follows a composite modal de possibili of which it is
the dictum.
These claims have a modern appearance: (i ) is a version of the Tarski
biconditional; (ii ) is like the law “T p → p”; (iii ) is like the law “p →
T p.” Equally, Theorem II-16 can be seen as expressing the distributive laws
“( p ∧ (p → q)) →
q” and “(♦p ∧ (p → q)) → ♦q.” Of course, Buridan
expresses these theorems as consequences, which are not simply conditionals
or rules of inference; nor is it strictly speaking correct to formalize his
logic with the propositional calculus, since no part of a sentence (such as
‘ p’) is a sentence (such as ‘p’), but merely contains a part equiform to a
sentence. These differences noted, Buridan’s claims are still quite similar to
the modern theses.
Finally, Buridan gives some mixing theorems which ‘mix’ composite
modals and divided modals. Theorem II-17 says that a particular affir-
mative divided modal follows from an affirmative composite modal (with
the dictum affirmed); Theorem II-18 says that a universal negative divided
modal follows from a universal composite modal (with the dictum denied).
These are the only consequential relations holding between composite and
divided modals.
8. The Syllogism
8.1 The Definition of the Syllogism
When we turn to syllogistic, it is necessary to recall that Buridan
is not working an artificial language and stating a symbolic calculus: he
is working a fragment of a natural language, although a highly stylized
fragment (scholastic Latin), and he possessed neither our modern array of
metalinguistic equipment nor our interest in formal metalogic. It is easy to
lose sight of these obvious facts, for Buridan’s syllogistic has an astonishing
degree of rigor.
In Buridan’s hands syllogistic is a logical instrument of great flexibil-
ity and power, not the rigid and sterile doctrine it later became; it is directly
based on his philosophical semantics. Buridan seems almost uninterested
in the part of assertoric syllogistic which most people have traditionally
identified as ‘syllogistic,’ quickly moving on to temporal syllogisms, oblique
syllogisms, variation syllogisms, and modal syllogisms (discussed Section
8.4).
The initial definition of ‘syllogism’ in TC 3.2.1 is given only after a
long description of what kind of consequence a syllogism is (TC 3.1.1–17).
The syllogism is a formal consequence, and in that sense syllogistic is merely
c Peter King, from Jean Buridan’s Logic (Dordrecht: D. Reidel 1985) 3–82.
INTRODUCTION TO JEAN BURIDAN’S LOGIC
65
a branch of the theory of consequences; it is distinguished by having a con-
junctive antecedent and a single consequent, made up with three terms.
This paradigm is generalized when Buridan turns to the oblique syllogism,
and allows more than three terms, provided that the terms connected in
the conclusion are parts of the terms of the premisses (TC 3.6.2–3), a result
required for variation syllogisms as well: more precisely, multiple-term syl-
logisms are permitted under strict assumptions about the relations of the
terms.
We can be more exact by introducing some of Buridan’s technical
terminology:
(1) The major sentence is the first premiss in the conjunctive antecedent,
and the minor sentence the second premiss in the conjunctive an-
tecedent (TC 3.2.3).
(2) The extremes of a sentence are its subject and predicate; the syllo-
gistic extremes are the extremes of the conclusion (TC 3.6.2).
(3) The syllogistic middle is a term or part of a term common to the
premisses; the major extreme is the extreme in the major premiss
which is not the syllogistic middle, and the minor extreme is the
extreme in the minor premiss which is not the syllogistic middle.
The major and minor extremes, or parts thereof, are connected in
the conclusion (TC 3.2.3 and 3.6.2).
When the syllogistic extremes are the major and minor extremes, and the
middle is the same term in both premisses, we have the additional paradigm
of the syllogism; the deviations above are introduced to allows for develop-
ment of the syllogistic.
We need three further technical notions to develop syllogistic. First,
we may define a syllogistic figure as the ordering of the syllogistic middle
to major and minor extreme in the premisses (TC 3.2.4); second, we call
a conclusion direct or indirect if the major extreme is predicated of the
minor extreme in the conclusion, or conversely; finally, we call a particular
pair of premisses characterized only with respect to quantity and quality a
conjugation.
From these definitions it is clear that there are exactly four figures
(TC 3.2 4–8): (1) the first figure, in which the syllogistic middle is subject
in the major sentence and predicate in the minor; (2) the second figure,
in which the syllogistic middle is predicate in major and minor; (3) the
third figure, in which the syllogistic middle is subject in major in minor; (4)
the fourth figure, in which the syllogistic middle is predicate in the major
sentence and subject in the minor. But if we transpose the premisses of the
fourth figure we have the first figure, changing the conclusion from direct
c Peter King, from Jean Buridan’s Logic (Dordrecht: D. Reidel 1985) 3–82.
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INTRODUCTION TO JEAN BURIDAN’S LOGIC
to indirect or conversely. Buridan correctly notes this point and does not
bother to treat the fourth figure independently (TC 3.2.9). He is quite
correct; given the way he has defined the syllogistic figures, they are not
really distinct; it is only on other definitions of the syllogistic figures that
there can be a genuine ‘fourth figure’ controversy.
89
8.2 Syllogistic Semantic Principles
A syllogism is a formal consequence with a conjunctive antecedent
and a single sentence as consequent, containing three or more terms. To
understand why a syllogism satisfies the Uniform Substitution Principle is
to understand the semantic framework of a syllogism, and this requires us
to examine how terms are conjoined—not merely in a single sentence but
across two sentences, the conjunctive antecedent. Buridan sets out this
semantic framework in two rules for the acceptability of syllogisms, which
require the notion of distribution.
Buridan’s two rules are given as his version of the traditional dic-
tum de omni et nullo, where one rule applies to syllogisms with affirmative
conclusions and the other to syllogisms with negative conclusions. His state-
ment is given in TC 3.4.5–7, but Buridan’s distinctions along the lines of
discrete and common terms are unnecessary. In their full generality they
are as follows:
[Rule 1] Any two terms which are called the same as a third term by
reason of the same thing for which that third term supposits, not
collectively, are correctly called the same as each other.
[Rule 2] Any two terms, of which one is called the same as some
third term of which the other is called not the same by reason of
the same thing of which that third term supposits, are correctly
called not the same as each other.
Two points must be noted: first, the ‘not collectively’ clause in Rule 1
excludes cases in which two terms are collectively or conjunctively called
the same as a third term, as when “matter and form are said to be the
same as one and the same composite, and the matter is not the same as
the form (TC 3.4.3).”
90
Second, the careful use of the phrases ‘called the
same’ and ‘called not the same’ indicate that Buridan is here talking in
what we should call the formal mode: they characterize sentences which, if
89
See the discussion of various definitions of the fourth figure and the related controver-
sies in Rescher [1966] Chapter II.
90
Two terms are used collectively if a sentence in which they are the conjoint subject
does not entail the conjunctive sentence in which each conjunct has only one of the
terms as the subject. See further Buridan’s discussion of collective terms in TS 3.2.3.
c Peter King, from Jean Buridan’s Logic (Dordrecht: D. Reidel 1985) 3–82.
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