78 GENERAL VIEW AND BASIS OF SCIENTIFIC RESEARCH. 



division, exclusion, combination, permutation, and trans- 

 formation into equivalents ; and as these properties largely 

 belong to the subject of inference, they will be illustrated 

 in Chapter XXXVI. on that subject. 



In logic, most terms have two meanings, viz., that 

 in extension and that in intension. A term employed in 

 the former sense means the objects to which the term can 

 be applied ; and when used in the latter, it means the 

 collection of essential qualities of the objects of th^t 

 name. A term ' in intension ' denotes individuals, and ' in 

 extension ' connotes qualities or circumstances. For in- 

 stance, the term ; metal ' means in extension either gold, 

 silver, copper, iron, or some other of the known metals, 

 but in intension it means the collection of essential 

 qualities which constitute a metal. 



Scientific terms are often in pairs, and are usually 

 classed into qualitative and quantitative, positive and 

 negative, privative, similar and contradictory, synonymous, 

 equivalent, absolute and relative, general and singular, in- 

 dividual, abstract and concrete, &c. 



Positive terms and ideas usually indicate the presence 

 or possession of a quality or attribute, and negative ones 

 usually signify the absence of that quality. For instance, 

 6 combustible ' and ' non-combustible, 5 ' darkness ' and 

 4 light ' are positive and negative terms respectively. Ne- 

 gative terms, however, sometimes indicate not the mere 

 absence of a quality or attribute, but the existence of one 

 of an opposite kind, for instance 'incombustibility.' 

 Every positive idea has its negative in thought, but there 

 does not always exist in language a suitable word to ex- 

 press it ; and positive terms have not always corresponding 

 negative ones. A negative term may be the name of all 

 things or ideas to which the corresponding positive one 

 cannot be applied. In a pair of logical terms, each is a 



