66 



(1) Metals conductors. 



(2) Not-metals conductors. 



(3) Not-metals not-conductors. 



It comes to the Ksame thing if we say that it excludes the 

 existence of the class metals not-conductors. But every 

 scientific process has its inverse process. As addition is 

 undone by subtraction, multiplication by division, differen- 

 tiation by integration, so logical induction is the inverse 

 process of deduction. Given certain classes of objects, we 

 endeavour by induction to pass back to the laws embodied 

 in those classes. There does not exist indeed any distinct 

 method of induction except such as consists in inverting the 

 processes of deduction, by noting and remembering the laws 

 from which certain eff^ects necessarily follow. The difficul- 

 ties of induction are thus exactl}^ analagous to those of 

 integration. 



As I have fully explained in my previous essays and 

 })apers, two terms or classes can be combined consistently 

 with the laws of thought in four different ways. Now out of 

 four such combinations sixteen selections (two to the power 

 four) can be made. As each distinct laAv gives a different 

 series of combinations, it follows that there could not pos- 

 sibly exist more than sixteen distinct forms of law governing 

 the combinations of two classes. But in one case, where all 

 the combinations remain, no special law applies ; in other 

 cases it can be shown that the combinations remaining are 

 so few as to imply self-contradiction. Only six sets of com- 

 binations require further consideration. By deductive exa- 

 mination it is found that four of these cases correspond to 

 varieties of the general form of law, A = AB, Avhicli ex- 

 presses the inclusion of the class A in the class B. By the 

 introduction of negative terms this general form may 

 receive four essentiall}^ different logical variations. Thus 

 we have 



