1^2 AN TIE NT METAPHYSICS. Bbok IT. 



jeS:, cannot be otberwife known to us, except by its operations on 

 pbyfical bodies ; (o tbat W€ muft firft ftudy and know thefe before we 

 can know what mind is. This obfervation applies particularly to the 

 queftion now before us, concerning the immateriality of fnind ; for 

 immaterial is a negative term, importing no more than that the fub- 

 je(fl to which we apply it, has not the qualities or affections of matter ; 

 for, with refpeCt to the eflence of either body or mind, as I have had 

 occafion to obferve more than once before, we know nothing ; all, 

 therefore, we can ki"iow of immaterial fubftances, is from matter. And 

 again, the properties of matter are only to be known by us from fenfe 

 and obfervation. It mufl: therefore be laid down as a pojlulatum in 

 this argument, that no qualities, properties, or laws of matter, are to 

 be fuppofed, which are not proved to exift by obfervation or experi- 

 rience. This is a rule of philofophifmg adopted by Sir Ifaac Newton, 

 and which, I think, ought to be invariably followed in all inquiries of 

 every kind concerning nature. 



But, tho* I adopt Sir Ifaac*s rule of philofophifing, T cannot fo rea*- 

 dily agree with what he lays down as laws of nature concerning body^ 

 particularly that law which aflerts, that there is a 'uis inertiae in matter 

 or hody^ (thefe two being the fame in the language of his philofophy) ; 

 for 1 hold it to be contrary to the rule of philofophifmg above men- 

 tioned which he has prefcribcd to himfelf ; becaufe it is evident, from 

 common obfervation, that every hody^ that we are acquainted with, is 

 either in motion^ or has a tendency to be in motion^ If, therefore, by 

 the 'VIS inertiae is meant a tendency in body to continue at reft, which 

 is the only proper meaning that can be given to the word, it is mani- 

 feftly repugnant to the phaenomena of nature ; fromwhicl;! it appears,, 

 that there is no body that has a tendency to reft : Or, if the meaning."^ 

 be, as I believe it is, that bodies perfevere in the motion that is given 

 them, either by nature or external impulfe, till fome contrary force 

 cither gives them another motion, or flops their motion altogether, 



the 



