EXPLANATORY SCIENCE 205 



such it is a special case of the problem of explanation. What 

 is to be emphasized here is that explanation is not to be 

 limited to one type. It is just as possible for the biological 

 and social sciences to become explanatory — though they 

 may require hypotheses of final causes and purposes — as it 

 is for the physical and mathematical sciences through the 

 application of notions of efficient cause, abstraction, and 

 analysis. 



Granting that explanation is approximately the sort of 

 thing which has been discussed, what may be said as to the 

 character of an explanatory science? Following the outline 

 of Chapter VII explanatory science may be considered from 

 the point of view (a) of extension, and (b) of intension. 



EXTENSIONAL FEATURES OF EXPLANATORY SCIENCE 



Extensionally explanatory science aims to represent both 

 (1) the clearly given events, and (2) those less clearly given 

 events which although conjectural as to status, are required 

 both for the purpose of rendering the clearly given events 

 " intelligible " and for the purpose of increasing the range of 

 our knowledge of such events. 



(1) The basic feature of explanatory science to be insisted 

 upon here is that such a science, in becoming explanatory, 

 does not cease to be descriptive. Every explanatory 

 science consists of two parts: (a) the descriptive proposi- 

 tions which constitute precisely the empirical science upon 

 which the explanatory science is founded, and (b) the 

 hypothetical propositions which characterize all of the 

 explanatory entities in terms of which the descriptive 

 propositions are to be rendered intelligible. These con- 

 stitute, respectively, the derived and the underived proposi- 

 tions, the theorems and the postulates, symbols of the kind X 

 and of the kind Y, as given in the diagram on page 198. 

 Every explanatory science, therefore, retains its descriptive 

 reference; it contains a number of propositions which are 

 capable of empirical verification. It is precisely these propo- 

 sitions out of which the explanatory science in its broader 



