Chap. II. ANTIENT METAPHYSICS. 77 



Brute, yet it is not effential to an Idea, but may belong alfo to a 

 Senfation. That philofophical language, therefore, among us, 

 which makes Generals and Ideas to be the fame thing, and fpeaks 

 of Ideas, Abftradt Ideas, and General Ideas, as all fynonimous 

 terms, is not accurate. 



There is a tJjird general obfervation concerning our Ideas, which 

 I hinted at in the preceding obfervation, but which it is proper to 

 explain more fully. It is this, That not only Subftances, or things 

 exifling by themfelves, fuch as Animals, Vegetables, or Bodies un- 

 organized, have their nature and eiTence which may be the fubject 

 of Ideas ; but alfo the qualities of fuch Bodies, fuch as hot and cold, 

 moift and dry, hard and foft, &c. have a certain nature and ef- 

 fence, which makes them operate in fuch and fuch a way upon the 

 organs of our fenfe, and produce fuch and fuch Senfatlons. And, 

 when we perceive that, then we have an Idea of that Senfation. 



There is anotlier general obfervation, I will make, which concerns 

 both our Ideas and Senfations, as it relates to the manner in which 

 we acquire our Senfations, compared with the manner of our ac- 

 quiring our Ideas. Our Senfations are produced by the impreffion 

 which external objedls make upon the organs of our Senfe. It is 

 by Motion, therefore, that we have our perceptions of Senfe ; and 

 this Motion muft: be different^ and confequently produce different 

 perceptions, according to the difpofition of the objedl, of the organ 

 or of the medium through which the objed: operates. On the other 

 hand, the Idea is not produced by the impulfe of any material ob- 

 jedls upon the organs of Senfe : It has, therefore, nothing to do 

 with Motion, but is fomething fixed and permanent, not fleeting; 

 and tranfitory like the perceptions of Senfe. This being the cafe it 

 is not to be wondered, that thofe philofophers of antiquity, men- 

 tioned by Plato in the Theactctes, fuch as Protagoras and Heracli- 

 tus, who maintained that all our knowledge was nothing but Senfa- 

 tions, maintained at the fame tinae that we had no knowledge that 



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