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
It must be admitted that Hamilton's account of the
matter when he is recommending the rejection of the modals,
is not by any means clear and consistent. He not only fails,
as already remarked, to distinguish between the formal and
the material (in other words, the true and the false) modality;
but when treating of the former he fails to distinguish
between the extremely diverse aspects of modality when
viewed from the Aristotelian and the Kantian stand-points.
Of the amount and significance of this difference we shall
speak presently, but it may be just pointed out here that
Hamilton begins (Vol. I. p. 257) by rejecting the modals on
the ground that the distinctions between the necessary, the
contingent, the possible, and the impossible, must be wholly
rested on an appeal to the matter of the propositions, in
which he is, I think, quite correct. But then a little further
on (p. 260), in explaining 'the meaning of three terms which
are used in relation to pure and modal propositions,' he gives
the widely different Kantian, or three-fold division into the
apodeictic, the assertory, and the problematic. He does not
take the precaution of pointing out to his hearers the very
different general views of logic from which these two accounts
of modality spring.[4]
6. There is one kind of modal syllogism which it
would seem unreasonable to reject on the ground of its not
being formal, and which we may notice in passing. The
premise 'Any A is probably B,' is equivalent to 'Most A are B.'
Now it is obvious that from two such premises as 'Most A
are B,' 'Most A are C,' we can deduce the consequence,
'Some C are B.' Since this holds good whatever may be
the nature of A, B, and C, it is, according to ordinary usage
of the term, a formal syllogism. Mansel, however, refuses to
admit that any such syllogisms belong to formal logic. His
reasons are given in a rather elaborate review[5] and criticism
of some of the logical works of De Morgan, to whom the
introduction of 'numerically definite syllogisms' is mainly
due. Mansel does not take the particular example given
above, as he is discussing a somewhat more comprehensive
algebraic form. He examines it in a special numerical
example:[6]--18 out of 21 Ys are X; 15 out of 21 Ys are Z;
the conclusion that 12 Zs are X is rejected from formal logic
on the ground that the arithmetical judgment involved is
synthetical, not analytical, and rests upon an intuition of
quantity. We cannot enter upon any examination of these
reasons here; but it may merely be remarked that his
criticism demands the acceptance of the Kantian doctrines
as to the nature of arithmetical judgments, and that it would
be better to base the rejection not on the ground that the
syllogism is not _formal_, but on the ground that it is not
_analytical_.
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