[325] This is another form of what will be found to be a special rule of figure 1, namely, that the major premiss must be universal. Compare section [244].
302 (4) Illicit process of the major is provided against indirectly. This fallacy can be committed only when the conclusion is negative; but the words “in like manner” declare that if there is a negative conclusion, the major premiss must also be negative; and since in any syllogism to which the dictum directly applies, the major term is predicate of this premiss, it will be distributed in its premiss as well as in the conclusion. Illicit process of the minor is provided against inasmuch as the dictum warrants us in making our predication in the conclusion only of what has been shewn in the minor premiss to be contained under the middle term.
(5) The proposition declaring that something is contained under the term distributed must necessarily be an affirmative proposition. The dictum provides, therefore, that the premisses shall not both be negative.[326]
[326] It really provides that the minor premiss shall be affirmative, which again is one of the special rules of figure 1.
(6) The words “in like manner” clearly provide against a breach of the rule that if one premiss is negative, the conclusion must be negative, and vice versâ.
EXERCISES.[327]
[327] The following exercises may be solved without any knowledge beyond what is contained in the preceding chapter, the assumption however being made that if no rule of the syllogism as given in section [199] or section [201] is broken, then the syllogism is valid.
210. If P is a mark of the presence of Q, and R of that of S, and if P and R are never found together, am I right in inferring that Q and S sometimes exist separately? [V.]
The premisses may be stated as follows:
All P is Q,
All R is S,
No P is R ;