Ch^. ir. ANTIENT METAPHYSICS. ij 



conceivable that they fhould both exift at the fame time ia the fame 

 fubjedt. 



As this argument, from the nature of relatives and of oppofites^ 

 may be thought by fome of my readers too metaphyhcal, I have, in 

 the chapter above quoted from the firft vol. of this work, p. 71. 

 given a proof from fadt and obfervation, which, I think, muft con- 

 vince every reader, though he be not a philofopher: For though he 

 may not beUeve that other motions, which he fees on this earth, are 

 produced by mind, yet 1 think he cannot doubt that the motions of 

 his own body are produced by his own mind ; and 1 have given, 

 in the paflage laft quoted, an example of it from a very fimple mo- 

 tion, viz. that of a man raifmg up his arm. Now, he muft know, 

 by the moft certain of ■ all knowledge, confcioufnefs, that the 

 arm does not move itfelf, but is moved by his mind willing that it 

 fhould be fo moved': And, accordingly, it is fo moved, though, by 

 the law of gravitation, it fhould, like other bodies, be moved down- 

 ward towards the earth.. 



Sir Ifaac Newton, I know, carried his fyftem, of all bodies being 

 moved either by themfelves or by other bodies impelling them, fo 

 far, that he maintained, as I have elfewhere obferved, that our 

 bodies are not moved by our mind, but by ethers and fluids, or by a 

 fpirhus fubtilijffimus, as he calls it in one palTage*. But here, I think, 

 his philolbphy is exceedingly defedive : For, in the jir/i place, he 

 does not prove that thcfe ethers or fubtile fluids do exift. idly^ If 

 he had proved their exiftence, he fhould have alfo proved that they 

 were, by fome caufe or another, put in motion ; for no body can 

 move another that is not firft moved itfelf. So that, in both thefe 

 refpeds, Sir Ifaae's philofophy of motion is exceedingly defedive. 



Bur 



* See his words quoted in vol. I. p. 275.— where he fays that the voluntary mo- 

 tion of animals is produced by a moft fubtile fpirit. 



