88 GENERAL VIEW AND BASIS OF SCIENTIFIC RESEARCH. 



statement can be a true one which contradicts any of the 

 laws of nature, true scientific ideas and statements are 

 not necessarily limited to existing things, because many 

 ideas and hypotheses have been proved to be true which 

 at the time they were propounded had no existing confir- 

 mation in nature. No proposition can be proved to be 

 universally true by means of experience alone, because 

 experience is finite. ' Experience can discover universal 

 truths, though she cannot give them universality.' l 



Affirmative propositions are usually the most im- 

 portant, and negative ones are often difficult or even 

 impossible to prove. An universal proposition is one 

 which affirms the predicate to belong to the whole of the 

 subject, such as ' All metals are conductors of heat.' A 

 particular proposition is one which affirms the predicate to 

 belong only to some or any part of the subject ; the pro- 

 position ' Some metals are lighter than mercury ' is a par- 

 ticular one. An indefinite proposition is one which does 

 not indicate whether the predicate belongs to the whole or 

 a part of the subject ; it is an ambiguous one, and incom- 

 plete as to matter of fact. 



An inconsistent proposition is one which disagrees 

 with some other proposition having the same subject and 

 predicate. Inconsistent propositions are inconsistent in 

 different degrees, and may be either contradictory, con- 

 trary, or sub-contrary. A contradictory one asserts what 

 is entirely inconsistent with some other proposition ; and 

 sub-contrary propositions have a less degree of contrariety 

 than contrary ones. Of two contradictory propositions, 

 if one is true the other must be false, and vice versa. Of 

 two contrary ones, both cannot be true, and both may be 

 false ; if one is false, the other may or may not be true. 



Whewell, History of Scientific Ideas, 3rd edit. vol. i. p. 270. 



