CHAPTER IV 



MECHANISM AND TELEOLOGY 



i. ON the surface, when we seek to explain any fact or 

 object of experience, we seem to ask sometimes one, 

 sometimes another of two very different questions. 

 The ' why ' of a thing means either its cause or its pur- 

 pose. Every explanation falls within one or other or both 

 of these categories, of which the one is known as the cate- 

 gory of mechanism, the other as that of teleology. Let 

 us consider the distinguishing characteristics of these two 

 categories, and to do so let us take a case where either 

 category is equally applicable. If we ask, for example, 

 the explanation of the motion of a given wheel or lever 

 in a machine, the answer may take two forms. First, it 

 may be pointed out that the lever performs a specific func- 

 tion in the machine, it opens and closes a valve, let us say, 

 which admits steam to a cylinder, and thereby governs the 

 working of the engine. This is a teleological explanation, 

 and that it is prima facie admissible in the present case 

 nobody doubts. Let us see to what questions we are led if 

 we pursue the enquiry on this side, if, that is, we follow the 

 teleological line. We shall see that this line divides into 

 two branches. On the one hand it leads us on into an 

 enquiry into the mechanism of the engine as a whole. Our 

 particular lever was, say, the eccentric that works a slide 

 valve. Having ascertained how the slide valve moves, 

 alternately opening and covering three apertures, we pro- 

 ceed next to the enquiry what this alternate process affects, 

 and thereby to the structure of the cylinder, the piston and 

 its connections on the one hand, and the steam pipe, boiler 



