CHAPTER X. 



OF THE POSSIBILITY OF MOTION IN GENERAL. 



THE doctrine of Heraclitus that all is a becoming was 

 unquestionably the most important phase of the pre- 

 Socratic philosophy. It unified the elements which had 

 previously been brought into definition, and which in the 

 Eleatic school were not only opposed to each other, but 

 were also held in mutual exclusion. The central doctrine 

 of Parmenides, the chief representative of that school, 

 was that "being alone is, and non-being is not." 



This doctrine involves the conception that everything 

 is all that it can ever be. It therefore has no potential 

 phase, and so can by no possibility pass out of its present 

 state. Hence no change, quantitative or qualitative, can 

 ever take place. All seeming change is mere illusion. 

 The senses only deceive us. It is by reason, and by 

 reason alone, that we can ever attain a knowledge of the 

 truth. The senses tell us that the things of the world 

 change ; reason assures us that no change whatever is 

 possible. 



Thus, in defense of this doctrine, Zeno's dialectic 

 comes to have an exclusively negative employment. Its 

 central, if not its sole, purpose is to prove that the con- 

 ception of motion (and hence of change) is a self -contra- 

 dictory conception, and hence impossible. A thing, he 

 says, must move either where it is or where it is not. 

 On the one hand, however, it is impossible that it should 



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