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INTRODUCTION TO JEAN BURIDAN’S LOGIC
matically common, for the term is used to refer to everything which it may
stand for. Buridan defines it as follows (TS 3.4.1):
Supposition is called ‘natural’ when a term indifferently supposits
for everything for which it can supposit, past and future as well
as present; this is the sort of supposition we use in demonstrative
science.
This definition is repeated in QNE 4.6 501:
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According to the older logicians, the common supposition of a term
is twofold: natural and accidental. . . it is [natural] when it sup-
posits indifferently for all of its supposits, whether past or future;
demonstrative science uses this supposition.
We may say, then, that a term has natural supposition if it supposits for
everything (past, present, future) which it signifies. As Buridan indicates,
he is reviving an old usage, for the logicians of the thirteenth century had
discussed natural supposition.
Buridan cites four reasons why we should admit natural supposition:
(i ) epistemic verbs require it (TS 3.4.3); (ii ) the disjunctive subject-terms of
sentences such as “What was or is or will be A is running” have it (TS 3.4.4);
(iii ) natural supposition is produced by terms such as ‘perpetually,’ ‘eter-
nally,’ and the like (TS 3.4.5); (iv ) demonstrative science uses it (TS 3.4.6–7
and QNE 6.6 501–502). Buridan argues that we can and do construct con-
cepts indifferent to time (TS 3.4.8–12 and QNE 6.6 501): our concepts
do not have any temporal reference, for it is possible to conceive a thing
“without understanding along with it a determinate time” (QNE 6.6 501).
Indeed, this is the only way our concepts can signify things of all times.
Natural supposition leaves us with a problem: cases like (i )–(iii )
quite obviously require omnitemporal reference, but in discussing (iv ) Buri-
dan cites sentences which do not have any clear indication of their natural
supposition, such as “Thunder is a sound in the clouds.” Buridan says that
such an utterance or inscription is properly subordinated to the Mental sen-
tence “Any thunder, whenever it was or is or will be, is or was or will be a
sounds in the clouds” (TS 3.4.7); in particular he calls the former sentence
an abbreviation (ad breviloquim) of the latter.
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the temporal quantifier
cides with the complete signification of the term, to its full or ‘natural’ extent.
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The formulation is close enough to be identified.
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In QNE 6.6 501 he says “This sentence ‘Man is an animal’ or ‘Every man is an
animal’ is about all [men] through natural supposition: of whatever and whenever it
is true to say ‘man’ then it is true to say ‘animal,’ and so ‘Thunder is a sound in
the clouds’ is true, by referring singulars to singulars.” I take this to be equivalent
to the reconstruction proposed above, and Scott [1965] to be in error in suggesting
c Peter King, from Jean Buridan’s Logic (Dordrecht: D. Reidel 1985) 3–82.
INTRODUCTION TO JEAN BURIDAN’S LOGIC
41
‘whenever’ has ‘it was or is or will be’ in its scope, and restricts the suppo-
sition of ‘thunder’ to times when thunder exists, for each case of which it
either was or is or will be a sound in the clouds (matching the times to the
tense of the copula). Buridan specifically rejects the conditional reading of
such sentences (502).
Hence whether a sentence such as “thunder is a sound in the clouds”
has natural supposition will depend on our understanding of the sentence,
that is, what the sentence corresponds to in Mental: the same Spoken or
Written sentence (or equiform sentences) may be ignored, doubted, opined,
and demonstratively known; to hold otherwise would be to make all knowl-
edge strictly a matter of semantics. Sentences of natural science are thus to
be understood as follows:
Socrates knows “Thunder is a sound in the clouds” (aparticular
utterance or inscription).
Socrates knows that any thunder, whenever it was or is or will be,
was or is or will be a sound in the clouds.
The latter expresses the Mental sentence to which the utterance or inscrip-
tion is subordinated. The Converse-Entailment Principle discussed in Sec-
tion 4.3 then licenses:
Thunder (whenever it was or is or will be) Socrates knows to have
been or to be or to be going to be a sound in the clouds.
Therefore for any instance of thunder Socrates knows it at least under the
ratio ‘sound-in-the-clouds’ (matching tenses appropriately). This removes
the difficulty about empty subject-terms, for the subject of this last sentence
is nonempty; indeed, it is ampliated to all and only those times at which
there is thunder.
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Supposition is accidental, on the other hand, when the supposition
of the term is not indifferent to time (TS 3.4.1), that is, refers to items
existing only at some determinate time or other (QNE 6.6 501). The re-
maining divisions of supposition apply only to accidental supposition, for
the restriction to a given time excludes some excludes some items from the
(putative) reference-class of the term.
that such sentences are disguised conditional statements. They are not, but rather
complex categoricals, as Buridan says.
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There is a further problem here: such a sentenced may have truth-at-all-times, by that
might not seem enough to capture the necessity involved in knowledge and science:
do we not need to require that every possible instance of thunder is equally a sound
in the clouds? Buridan does not mention this. On his behalf we might suggest either
(i ) natural supposition includes ampliation to possibles; (ii ) there are no never-actual
possibles—but each suggestion obviously has further problems.
c Peter King, from Jean Buridan’s Logic (Dordrecht: D. Reidel 1985) 3–82.