body has absorbed such an amount of arsenic, it must be true that the man is dead; whereas the mere fact of his death does not prove that many another possible cause is not the actual cause. In short, 'The man is dead' is logically prior to the proposition, the tissues of his body have absorbed the required quantity of arsenic." (This is the whole of passage (a). Passage (c) is much more general, but contains nothing to clash with it.)
Every one sees at once that we are here dealing with the relation of antecedent to consequent in a normal hypothetical judgment, where implication is stated according to the traditional rule which governs all implication and conversion in Formal Logic. Truth of antecedent implies truth of consequent; truth of consequent does not imply truth of antecedent. It is the same view of implication which admits plural or alternative causes,[1] as indeed the above passage insists.
If we now extend our consideration to passage (b) (p. 112), we see that, though the writer does not remark upon the question of Logical Priority, yet he treats precisely the same implications as holding good, in accordance with the ordinary rule, between the pair of premisses of a syllogism and its conclusion. The truth of the two premisses implies that of the conclusion. The truth of the conclusion does not imply that of the two premisses. In this respect conclusion is to premisses as consequent to
- ↑ Note that on p. 112 Causal Dependence is assumed to be reciprocal. And cf. p. 225.
