THE NEEWTONIAN PHILOSOPHY. 535 



be demonftrated a priori. Now, to determine this, we muft know the 

 nature and eflence of this thing we call matter ; for, knowing it, we 

 fhall know whether motion be efTential to matter or not ; and, if we 

 difcover it to be efTential, we fhall know, with great certainty, frft^ 

 that it moves itfelf, 2iud,Jecondly^ that the motion is eternal, and does 

 continue as long as the matter exifts ; whereas, on the contrary, if we 

 find that it is not efTential to matter, but adventitious, then we fhall 

 know, with equal certainty, that matter does not move itfelf, and that, 

 as it is moved by fomething of a nature foreign to it, there is no necef- 

 fity to fuppofe that the motion will be eternal. Now, this, as I have 

 faid, is certainly a metaphyfical queftion ; for matter, abftra(3:ed from 

 form^ and from Mind^ which gives it its form and qualities of every 

 kind, is altogether a metaphyfical entity. 



Before I begin this inquiry, I cannot help obferving, that a man 

 who has fludied the antient philolbphy, will be furprifed to find two 

 things, of natures fo different as reft and motion, fo much confounded 

 as they are, in this law of motion ; for the pruiciple, both of reft and 

 motion, is made to be the fame, viz. the vis infita^ or vis inertias^ as it 

 is called, by which the body continues both at refl and in motion. 

 Now, it appears, that reft and motion are not only different in their 

 natures, but altogether oppofite ; for a body at reft does not change its 

 place, and neither aQ:s, nor is aded upon ; whereas, a body that 

 is moved, goes through fpace, and is certainly a6ted upon ; and, if fo, 

 there muft be fomething that atfts, and, if there be any thing in its 

 way, the body itfelf adts, by moving out of the v^ay the obftacle to its 

 motion. How, then, a ftatc of motion and reft can be compared to- 

 gether, and the fame principle applied to both, is what I cannot con- 

 ceive. I cannot, therefore, fuppofe, tliat, becaufe a body at reft conti- 

 nues at reft, till it be excited to motion by fomething external, there- 

 fore a body, in a ftatc fo different from that of motion, continues in 

 motion till it be ftopped by fomething external. A man, too, who is 



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