THE METAPHYSICS OF SENSATION 259 



the localization of that sensation is an act of the 

 mind, how is it conceivable that a relation be- 

 tween two localized sensations should exist apart 

 from the mind ? It is, I confess, quite as easy 

 for me to imagine that redness may exist apart 

 from a visual sense, as it is to suppose that 

 co-existence, number, and distance can have any 

 existence apart from the mind of which they are 

 ideas. 



Thus it seems clear that the existence of some, 

 at any rate, of Locke's primary qualities of matter, 

 such as number and extension, apart from mind, 

 is as utterly unthinkable as the existence of colour 

 and sound under like circumstances. 



Will the others namely, figure, motion and 

 rest, and solidity withstand a similar criticism ? 

 I think not. For all these, like the foregoing, are 

 perceptions by the mind of the relations of two or 

 more sensations to one another. If distance and 

 place are inconceivable, in the absence of the mind 

 of which they are ideas, the independent existence 

 of figure, which is the limitation of distance, and of 

 motion, which is change of place, must be equally 

 inconceivable. Solidity requires more particular 

 consideration, as it is a term applied to two very 

 different things, the one of which is solidity of 

 form, or geometrical solidity ; while the other is 

 solidity of substance, or mechanical solidity. If 

 those motor nerves of a man by which volitions 

 are converted into motion were all paralysed, and 



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