292 ELEMENTS OF SCIENCE 



When a universal affirmative and a particular nega- 

 tive (A and 0) or a particular affirmative and a universal 

 negative (I and E) are opposed, they are " contradictories," 

 because they differ both in quantity (one being universal 

 and the other particular), and also in quality (one being 

 affirmative and the other negative) : e.g., " All men are 

 reasonable beings" and "some men are not reasonable 

 beings," or " Some men are able to rise in the air " and 

 " no men are able to rise in the air." With contradic- 

 tories, both cannot be true and both false, but always one 

 true and the other false. 



When a universal affirmative and a universal negative 

 (A and E) are opposed they are termed " contraries." 

 They differ from each other in quality only and not 

 in quantity, because they are both universals ; as e.g., 

 "All plants are sensitive" and "no plants are sensi- 

 tive." Contraries may both be false, but they cannot 

 both be true. 



When a particular affirmative is opposed to a particular 

 negative (I and 0) they are called " subcontraries " and 

 differ as to quality only, both being particular, and 

 therefore the same in quantity; as e.g., "Some men 

 are soldiers " and " some men are not soldiers." 

 Subcontraries may both be true, but they cannot both 

 be false. 



When a universal affirmative and a particular affirm- 

 ative (A and I), or a universal negative and a particular 

 negative (E and 0) are opposed, they are named "sub- 

 alterns." They are opposed in quantity only (each pair 

 consisting of one universal and one particular proposition) 

 and not in quality (one pair being both affirmative and 

 the other pair both negative) ; as e.g., " All men are 

 mortal" and " some men are coal-heavers," or " No men 

 have tails " and " some men have not snub-noses." 



