CHAPTER II. 

 CLASSIFICATION AND COMPARISON OF THEORIES. 



I have found in considering the theories stated that they may be 

 conveniently classified from two points of view. When viewed from 

 the point of view of method of procedure in deriving the theory, there 

 are two distinct classes; and when viewed with respect to the nature 

 of the problem solved as a basis, there are two well defined classes. 



We shall first consider the classes of theories from the view-point 

 of problem solved. The first class of theories under this head con- 

 sists of those which have for their object to explain the origin or 

 existence of things or relations between things by showing the manner 

 in which these things or relations were produced. Darwin's theory of 

 "The Origin of Species" falls under this class. His problem was to 

 explain how well defined species of animals and plants came to be 

 formed; and his solution consisted in showing that individual varia- 

 tions with natural selection would give rise to species in nature as 

 similar processes do in case of domesticated animals. Hyslop's prob- 

 lem and solution were of the same nature. He sought to explain the 

 origin of supernormal knowledge, and did so by inferring that spirits 

 of departed persons, who were possessed of the knowledge in question, 

 still existed and imparted the information through the living medium. 

 So also the theory of ions belongs to this class. The problem there 

 was to explain the origin or existence of the well defined relation- 

 ships existing between the chemical elements, and expressed by the 

 Periodic Law. The relationships were explained by showing the 

 complexity of the atom and the periodic variation in the number and 

 arrangement of the ions in the atom. And lastly, the theory of 

 Inorganic Evolution has the same kind of problem and solution. 

 The problem was to explain the existence of the many elements in 

 nature and their origin. The solution consisted in showing the trans- 

 formation from one element into another with varying degrees of 

 temperature. Thus these theories illustrate a class in which the 

 question is asked: how came certain things or relations to be? and is 

 answered by revealing the process of origin. 



Now there is from the point of view of problem and method of 

 solution, a second class of theories. Those theories which seek to 

 determine the essential qualities of things or relations by defining 

 them. John Locke in his Theory of Human Knowledge, seeks to 



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