CHAPTER II. 

 GENERAL RULES OR CANONS OF THE SYLLOGISM. 



154. DERIVATION OF THE GENERAL RULES OR CANONS 

 FROM THE DICTUM. We have pointed out that the Dictum de 

 omnietnullo applies directly only to syllogisms in which the middle 

 term is subject in the major premiss and predicate in the minor 

 premiss. The middle term may, however, occupy other positions, 

 thus giving rise to other forms or &quot; figures&quot; (159) of the syl 

 logism. 



If the Dictum be analysed it will be found to involve a 

 number of requirements which are usually stated as general rules 

 or canons of the syllogism, and which are directly and immedi 

 ately applicable to all figures of the categorical syllogism. These 

 latter being all reducible to the Aristotelean figure, it will need 

 only a little generalization of the special requirements of the 

 Dictum to make the rules so derived applicable to the syllogism 

 whatever the position of the terms may be. 



(1) Thus, the Dictum mentions three and only three terms: 

 &quot;whatever is &quot;predicated&quot;; &quot;the class-concept of which it is 

 predicated &quot; ; &quot; what is asserted to belong to that class &quot;. Hence 

 the rule : A syllogism must have three and only three terms. 



(2) Similarly, the Dictum mentions three and only three com 

 parisons or propositions. Hence the rule : A syllogism must have 

 three and only three propositions. 



(3) The Dictum says that something must be predicated 

 distributively about a logical whole or c/ass-concept. This latter 

 is the middle term, occurring as subject of the major premiss. 

 The Dictum therefore demands that the middle term be distributed 

 in the major premiss. Generalizing this, so that it will apply to 

 all forms of syllogism, we have the rule : The middle term must be 

 distributed in one at least of the premisses. 



(4) The Dictum says that the original predication can be 

 made [in the conclusion] of &quot; anything &quot; [S] which can be asserted 



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