348 PERSONAL PREPARATION FOR RESEARCH. 



seems unnecessary to make it. It is, however, advan- 

 tageous if not necessary, because it renders explicit what 

 was previously only implicit ; and anything which brings 

 knowledge into view or adds to the clearness of our ideas 

 is a mental advantage. It also gives us, more or less, 

 new information ; for instance, in the example just given 

 (which appears like a mere repetition) nothing is said 

 about ' conductors of electricity ' in the original proposi- 

 tion, but by means of each of the inferences given we 

 obtain explicit information respecting them. 



All knowledge is relative ; a truth never stands alone. 

 It is impossible to make any affirmative statement without 

 supplying the means of drawing inferences respecting the 

 positive and negative ideas implied in it ; and in this way 

 known truths enable us, by means of immediate inference, 

 to evolve new truths from them, and thus make new dis- 

 coveries, and add to our stock of new knowledge. 



The several modes of immediate inference, known by 

 the names of inference by privative conception, by added 

 determinants, and by complex conception, &c., are de- 

 scribed and illustrated in various works on logic. 1 



In cases where we can compare two things directly 

 with each other, we employ one proposition only, consist- 

 ing of two terms, and in drawing a conclusion or second 

 proposition from it we reason by ' immediate ' or < direct ' 

 inference. But there are very many things or ideas which 

 can only be compared in an indirect manner, i.e. by means 

 of a third idea or object, and in those more difficult cases 

 two propositions are employed, and in drawing a con- 

 clusion or third proposition from them we reason by 

 6 mediate/ or ' syllogistic ' inference. For instance, if we 

 cannot compare two objects together side by side, to ascer- 

 tain if they are similar in dimensions, colour, or any other 

 1 See Jevons, Elementary Lessons on Logie, p. 85. 



