CHAPTER VI 



THE GEOMETRY OF MOTION 



^ I . — Motion as the Mixed Mode of Perception 



We have seen in the previous chapter that there are two 

 modes under which the perceptive faculty discriminates 

 between the contents of perception, namely, those of space 

 and time. The combination of these two modes, to 

 which we give the various names of change, motion, 

 growth, evolution, may be said to be the mixed mode 

 under which all perception ta"kes place/ Science, accord- 

 ingly, if we except special branches treating of the modes 

 under which we perceive and think, is essentially, as a 

 description of the contents of perception, a description of 

 change or variation. In order to draw a mental picture 

 of the universe, to map out in broad outline its character- 

 istics, science has introduced the conception of geometrical 

 forms ; in order to describe the sequence of perceptions, 

 to form a sort of historical atlas of the universe, science 

 has introduced the conception of geometrical forms 

 changing with absolute time. The analysis of this con- 

 ception is what we term the Geometry of Motion. The 

 geometry of motion is thus the conceptual mode in which 

 we classify and describe perceptual change. Its validity 



^ Trendelenburg sees in real or constructive motion the basis of all per- 

 ception and conception. lie tries to show that the conception of motion does 

 not require the notions of space and time, which he asserts flow from the concep- 

 tion of motion itself. I do not think he is successful in this, but his attempt is 

 instructive as showing how essentially perception and conception involve 

 motion. (See his Logische Utttersuchmigen, 2nd edition, Bd. i. chaps, v. -viii. 

 Leipzig, 1862.) 



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