ONT Re: De In Esse Predication
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DEIP. Note 9
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| The question is what is the sense which is most usefully attached
| to the hypothetical proposition in logic? Now, the peculiarity of
| the hypothetical proposition is that it goes out beyond the actual
| state of things and declares what 'would' happen were things other
| than they are or may be. The utility of this is that it puts us in
| possession of a rule, say that "if A is true, B is true", such that
| should we hereafter learn something of which we are now ignorant,
| namely that A is true, then by virtue of this rule, we shall find
| that we know something else, namely, that B is true.
|
| There can be no doubt that the Possible, in its primary meaning,
| is that which may be true for aught we know, that whose falsity
| we do not know. The purpose is subserved, then, if throughout
| the whole range of possibility, in every state of things in
| which A is true, B is true too.
|
| The hypothetical proposition may therefore be falsified
| by a single state of things, but only by one in which A
| is true while B is false. States of things in which A
| is false, as well as those in which B is true, cannot
| falsify it.
|
| If, then, B is a proposition true in every case
| throughout the whole range of possibility, the
| hypothetical proposition, taken in its logical
| sense, ought to be regarded as true, whatever
| may be the usage of ordinary speech.
|
| If, on the other hand, A is in no case true, throughout the
| range of possibility, it is a matter of indifference whether
| the hypothetical be understood to be true of not, since it is
| useless. But it will be more simple to class it among true
| propositions, because the cases in which the antecedent is
| false do not, in any other case, falsify a hypothetical.
| This, at any rate, is the meaning which I shall attach
| to the hypothetical proposition in general, in this
| paper.
|
| C.S. Peirce, 'Collected Papers', CP 3.374,
|"On the Algebra of Logic: A Contribution to the Philosophy of Notation",
|'American Journal of Mathematics', vol. 7, no. 2, pp. 180-202, 1885.
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