LOGIC 305 



This is a syllogism of the third figure and the mood 

 A A A, but there is no valid mood of that kind in the 

 third figure which needs a particular, not a universal, 

 conclusion. The Above apparent syllogism is invalid- 

 There is in it an " illicit process of the minor," the term 

 " long-lived men " not being distributed in the minor 

 premiss, though it is in the conclusion. 



A Demonstration is a syllogism, the major term of 

 which denotes a "property," the minor the "species," 

 and the middle term the definition* of a species. 

 Thus: 



A rational animal is capable of laughter. 



Man is a rational animal. 



Therefore man is capable of laughter. 



But all syllogisms are objected to by some people who 

 affirm that they teach us nothing, because the conclusion 

 of a syllogism only re-affirms what was already contained 

 in its premisses. " Whoever has said," they repeat, that 

 " all men are mortal " has already said in effect that 

 "Socrates is mortal." 



To test the force of this objection, let us see by an 

 example what our meaning is when we declare that any 

 one object belongs to a certain class of objects. Persons 

 ignorant of zoology, may fancy that a whale is a fish. 

 Nevertheless the whale in truth belongs to the class of 

 beasts. Now when we make that statement what do we 

 mean ? We mean that a whale, in spite of its shape and 

 exclusively marine mode of life, is nevertheless more 

 closely allied in its nature to such creatures as cattle, 

 beasts of prey, &c., than it is to any fishes. But even if 

 we are zoological experts, we do not, in saying " a whale 



* See ante, p. 288. 



