CHAPTER XXIV. 



EMPIRICAL KNOWLEDGE, EXPLANATION, AND PREDICTION. 



INDUCTIVE investigation, as we have seen, consists in the 

 union of hypothesis and experiment, deductive reasoning 

 being the link by which experimental results are made to 

 confirm or confute the hypothesis. Now when we consider 

 this relation between hypothesis and experiment it is 

 obvious that we may classify our knowledge under four 

 heads. 



(1) We may be acquainted with facts which have not 

 yet been brought into accordance with any hypothesis. 

 Such facts constitute what is called Empirical Knowledge. 



(2) Another extensive portion of our knowledge consists 

 of facts which having been first observed empirically, 

 have afterwards been brought into accordance with other 

 facts by an hypothesis concerning the general laws apply- 

 ing to them. This portion of our knowledge may be said 

 to be explained, reasoned, or generalised. 



(3) In the third place comes the collection of facts, minor 

 in number, but most important as regards their scientific 

 interest, which have been anticipated by theory and after- 

 wards verified by experiment. 



(4) Lastly, there exists knowledge which is accepted 

 solely on the ground of theory, and is incapable of experi- 

 mental confirmation, at least with the instrumental means 

 in our possession. 



It is a work of much interest to compare and illustrate 

 the relative extent and value of these four groups of know- 

 ledge. We shall observe that as a general rule a great 

 branch of science originates in facts observed accidentally. 



