THE MEANING OF PERCEPTION 191 



any intuition corresponding with freedom of mobility in a fourth 

 dimension. Clearly in developing four-dimensional gecmetiy 

 mathematicians are trying to remove a mental constraint from 

 their space intuitions. 



Our notion of space is not, then, a " form of our sensibility " so 

 much as an intuition, or feeling of our freedom to move in the 

 ways that are possible to us. " Abstract space " is not an 

 absolute something which we contemplate, but it is just the way 

 in which we describe our mobility of body assuming, of course, 

 that this has become equally well developed in three dimensions. 

 Neither is time something absolute which we live through. 

 When we speak about it and measure it we do nothing more than 

 observe certain simultaneously occurring events. Last night, 

 when the hands of the clock pointed to twelve midnight, a certain 

 star crossed the meridian, and to-night, after the hour hand of tht 

 clock has twice turned through 360, the same star again crosses 

 the meridian. The time here is a space measurement, but there 

 is something else. We had to live through that space measure- 

 ment, if one may say so, and our intuition of time past is our 

 mental duration. If we had no memory, all that we should know 

 would be the appearances of the star on the cross wires of the 

 telescope simultaneously with the positions of the hands of the 

 clock indicating twelve midnight. But we remembered the lapse 

 of twenty-four hours because, during that period, our perceptions 

 have endured as memory. 



This matter, however, we consider in the following chapter. 

 Meanwhile, we have suggested to the reader an interpretation of 

 the Kantian categories, which seems to be that forced upon us 

 by the study of biology. These mental operations are not " pure 

 conceptions of the understanding," the latter being thought 

 about as something sitting still and apart from the body, so to 

 speak, and contemplating the universe through the sense organs. 

 They are nascent or virtual actions of the body, each of which 

 changes in some way the system which is made up of the body 

 and the universe. In thinking and employing the categories of, 

 say, quantity and substance, we are really acting schematically. 

 Let an analogy make this clear : a man who moves a little lever, 

 and so actuates a hydraulic ram, is not really lifting an enormous 

 weight, nor does a signalman move the trains that pass over a com- 

 plicated system of junctions. So the categories of the understand- 

 ing are the ways in which we turn stimuli (the " sensible objects of 

 perception ") into the bodily mechanisms that we will to respond. 



