THE NATURE OF INFERENCE. 137 



does it destroy, but it transmutes and throws the same 

 matter into a new form. 



The difficult question still remains, Where does novelty 

 of form begin ? Is it a case of inference when we pass 

 from f Sincerity is the parent of truth ' to * The parent of 

 truth is sincerity V The old logicians would have called 

 this change conversion, one case of immediate inference. 

 But as all identity is necessarily reciprocal, and the very 

 meaning of such a proposition is that the two terms are 

 identical in their signification, I fail to see any difference 

 between the statements whatever. As well might we say 

 that a = b and b = a are different equations. 



Another point of difficulty is to decide when a change 

 is merely grammatical and when it involves a real logical 

 transformation. Between a table of wood and a wooden 

 table there is no logical difference (p. 37), the adjective 

 being merely a convenient substitute for the prepositional 

 phrase. But it is uncertain to my mind whether the 

 change from ' All men are mortal ' to ' No men are not 

 mortal' is purely grammatical. Logical change may 

 perhaps be best described as consisting in the determina- 

 tjon. of a relation between certain classes of objects from 

 a relation between certain other classes. Thus I consider 

 it a truly logical inference when we pass from ' All men 

 are mortal ' to ' All immortals are not-men/ because the 

 classes immortals and not-men are different from mortals 

 and men, and yet the propositions contain at the bottom 

 the very same truth, as shown in the combinations of the 

 Abecedarium. 



From logical inference we must discriminate the passage 

 from the qualitative to the quantitative form of a pro- 

 position. We state the same truth when we say that 

 'mortality belongs to all men,' as when we assert that 

 * all men are mortals/ Here we do not pass from class to 

 class, but from one kind of term, the abstract, to another 



