The Logic of Chance, 3rd edition: An Essay on the Foundations and Province of the Theory of Probability, With Especial Reference to Its Logical Bearings and Its Application to Moral and Social Science and to StatisticsVenn, John
Philosophy
The Logic of Chance, 3rd edition: An Essay on the Foundations and Province of the Theory of Probability, With Especial Reference to Its Logical Bearings and Its Application to Moral and Social Science and to Statistics
Venn, John
Chance; Logic, Symbolic and mathematical; Probabilities; Science -- Methodology
3. I allude of course to such examples as 'A killed B unjustly,' in
which the killing of B by A was sometimes said to be asserted not
simply but with a modification. (Hamilton's _Logic_, I. 256.) It is
obvious that the modification in such cases is by rights merely a
part of the predicate, there being no formal distinction between 'A
is the killer of B' and 'A is the unjust killer of B.' Indeed some
logicians who were too conservative to reject the generic name of
modality in this application adopted the common expedient of
introducing a specific distinction which did away with its meaning,
terming the spurious kind 'material modality' and the genuine kind
'formal modality'. The former included all the cases in which the
modification belonged by right either to the predicate or to the
subject; the latter was reserved for the cases in which the
modification affected the real conjunction of the predicate with the
subject. (Keckermann, _Systema Logicæ_, Lib. II. ch. 3.) It was, I
believe, a common scholastic distinction.
For some account of the dispute as to whether the negative particle
was to be considered to belong to the copula or to the predicate,
see Hamilton's _Logic_, I. 253.
4. He has also given a short discussion of the subject elsewhere
(_Discussions_, Ed. II. p. 702), in which a somewhat different view
is taken. The modes are indeed here admitted into logic, but only
in so far as they fall by subdivision under the relation of genus
and species, which is of course tantamount to their entire
rejection; for they then differ in no essential way from any other
examples of that relation.
5. _Letters, Lectures and Reviews_, p. 61. Elsewhere in the review
(p. 45) he gives what appears to me a somewhat different decision.
6. It must be remembered that this is not one of the proportional
propositions with which we have been concerned in previous chapters:
it is meant that there are _exactly_ 21 Ys, of which just 18 are X,
not that on the average 18 out of 21 may be so regarded.
7. I consider however, as I have said further on (p. 320), that the
treatment in the older logics of Probable syllogisms, and Dialectic
syllogisms, came to somewhat the same thing as this, though they
looked at the matter from a different point of view, and expressed
it in very different language.
8. The distinction is however by no means entirely neglected. Thus
Smiglecius, when discussing the modal affections of certainty and
necessity, says, "certitudo ad cognitionem spectat: necessitas vero
est in re" (_Disputationes;_ Disp. XIII., Quæst. XII.).
9. It may be remarked that Whately (_Logic_, Bk. II. ch. II. §2)
speaks of necessary, impossible and contingent matter, without any
apparent suspicion that they belong entirely to an obsolete point of
view.
10. _Formal Logic_, p. 233.
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