422 ANT I EN T METAPHYSICS. BookV. 



ference here, betwixt the reed Caufe and the fuppofed Caufe, is, tliat 

 the real Caufe arifes from the nature of the Planetary Motion, which, 

 hke every other Motion, confifts of two things, ^/y?. The Moving 

 Force or Velocity ; and, ^dIy^ The Diredion of that Force in an 

 Orbit of fuch a Curvature. The real Caufe therefore of this 

 Defcent, is the nature of the Planetary Motion in which it is in- 

 lierent, and with which it is enentially conneded; whereas the 

 Caufe \ fuppofc is, a Motive Force not neceflarily joined with the 

 reft of the Planetary Motion, but feparatcd and a£ting by itfelf. — 

 So that by my Hypothecs I do no more than divide and confidcr, 

 feparately, what by Nature is neceflarily joined. This, I fay, is the 

 Method of all Science; and I maintain, liiat without fuch Abftra£tions 

 no Science could be properly taught. Proceeding in this way, Euclid 

 has abftraded Length from Breadth, and both from Depth, and all 

 the three from Body. When Euclid does fo, he p'oceeds upon an 

 hypothefis, as well as I do in this cafe ; for, as I fuppofe that 

 there is a feparate Motive Power, which makes the Body defcend 

 from the Tangent, fo he fuppofes that Length, Breadth, and Depth, 

 have a feparate exiftencc by themfelves, which is certainly not true 

 in fa£t \ but no body will fay his demonftrations are lefs conclufive 

 becaufe they proceed upon this hypothefis. In the fame manner 

 T fay that Projedion and Gravitation, though they have no feparate 

 exiftence by themfelves, are inherent in the Planetary Motion as 

 much as Length, Breadth, and Depth are in Body; and therefore 

 that Sir Ifaac's Demonftrations are as certain upon the Hypothefis 

 of the Separate Exiftence of Projedlion and Gravitation, as Euclid's 

 are upon the Hypothefis of the Separate Exiftence of Length, 

 Breadth, and Depth. — And it may be obfer\'ed, that there is this 

 difference betwixt my hypothefis and that of Euclid, that it is im- 

 pofTible, by the nature of things, that Length, Breadth, and Depth, 

 can exift feparately ; whereas no body will deny, at leaft no New- 

 tonian, that the two Motions I have ftippofcd may have a feparate 

 exiftence, and be combined together, to form the Planetary Motion. 



Having 



