THE THEORY OF CONTINUITY 145 



speak of becoming " better acquainted," as for instance 

 with a person, what we must mean is, becoming 

 acquainted with more parts of a certain whole ; but the 

 acquaintance with each part is either complete or non- 

 existent. Thus it is a mistake to say that if we were 

 perfectly acquainted with an object we should know all 

 about it. " Knowledge about " is knowledge of pro- 

 positions, which is not involved necessarily in acquaintance 

 with the constituents of the propositions. To know that 

 two shades of colour are different is knowledge about 

 them ; hence acquaintance with the two shades does not 

 in any way necessitate the knowledge that they are 

 different. 



From what has just been said it follows that the nature 

 of sense-data cannot be validly used to prove that they 

 are not composed of mutually external units. It may be 

 admitted, on the other hand, that nothing in their 

 empirical character specially necessitates the view that 

 they are composed of mutually external units. This 

 view, if it is held, must be held on logical, not on 

 empirical, grounds. I believe that the logical grounds 

 are adequate to the conclusion. They rest, at bottom, 

 upon the impossibility of explaining complexity without 

 assuming constituents. It is undeniable that the visual 

 field, for example, is complex ; and so far as I can see, 

 there is always self-contradiction in the theories which, 

 while admitting this complexity, attempt to deny that it 

 results from a combination of mutually external units. 

 But to pursue this topic would lead us too far from our 

 theme, and I shall therefore say no more about it at 

 present. 



(e) It is sometimes urged that the mathematical 



account of motion is rendered fictitious by its assumption 



of points and instants. Now there are here two different 



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