LOGIC. 79 



perate. In modal propositions, the copula or verb is qualified ; as, 

 Brutus killed Ceesar justly. A. compound proposition has two or 

 more subjects, or predicates ; and may be resolved into two or more 

 simple propositions. 



As regards quantity, propositions are either universal or particu- 

 lar ; and as regards their quality, or nature, they are either affirmative 

 or negative. Hence arise four kinds of Propositions, which are de- 

 signated, in Books of Logic, by the first four vowels ; and named, as 

 in the following examples. 



A. Every war is just. Universal Affirmative. 

 E. Every war is unjust. Universal Negative. 

 I. Some wars are just. Particular Affirmative. 

 O. Some wars are unjust. Particular Negative. 



Referring to these forms, when compared together, A and E are termed 

 Contraries: I and 0, Subcontraries : A and O, or I and E, Contra- 

 dictories ; and A and I, or E and O, are termed Subalterns. From this, 

 it will be seen, that two Contraries cannot both be true, though they 

 may both be false ; two Subcontraries may both be true, but not both 

 false; two Contradictories cannot both be true, nor yet both false; and 

 of two Subalterns, the particular is true if the universal is, but the 

 particular may be true, and the universal false. In the Conversion of 

 a proposition, or making the subject and predicate change places, care 

 must be taken to restrict the terms to their first or original meaning. 



3. A Syllogism, is an argument, stated, as every argument 

 may be, in a regular Logical form ; as, All tyrants deserve death : 

 Caesar was a tyrant ; therefore he deserved death. An argument, 

 technically defined, is a process of Reasoning, or of inference, in 

 which something is concluded or proved, by the comparison of certain 

 conditions or data. The use of a syllogism, is to test the correctness 

 of an argument, in difficult or doubtful cases ; in which, though often 

 contemned, it is an instrument of real importance. It should be ob- 

 served, however, that not only must the process of reasoning be legi- 

 timate, but the data, to which it is applied, must also be correct, in 

 order to insure a correct conclusion. Every syllogism consists of 

 three propositions, expressed or implied ; two of which are given, and 

 called the premises, or data ; while the third, which, before being 

 proved, was called the question, becomes, when proved, the conclu- 

 sion or inference. A syllogism necessarily contains only three terms ; 

 each being twice employed. In the example, 



Every plant is combustible : 



Every Le is a plant; 



Therefore, every tree is combustible. 



Plant is the middle term, because found in both the premises ; tree 

 is the minor term, found in the second or minor premiss ; and com- 

 bustible is the major term, which is always the predicate of the con- 

 clusion. If one of the premises be negative, the conclusion, if there 

 be any, must be negative also. 



The figure of a syllogism, has reference to the place of the middle 

 term ; and the mood depends upon the kinds of propositions, among 



