33<3 ANTIENT METAPHYSICS. Book V. 



thing of this Axiom, as it is called, the negative argument would be 

 fufficient to prove. That there is nothing like it to be found in all the 

 writings, or in any accounts, that we have of the opinions of their 

 philofophers concerning natural things. But, befides this, there is 

 pofitive evidence that Ariftotle at lead knew nothing of the matter. 

 This appears from a paffage above quoted concerning Dreams, and 

 from another in his book De Naturali Aufcultatione *. 



But this propofition, whether true or falfe, is fo far, in my ap- 



prehenfion, from being an Axiom, that it is impoffible to judge of 



the truth of it, without knowing accurately the nature both of Body 



and of Mind, and likewife of Motion ; to know whicTi certainly 



does not belong either to Geometry or Mechanics, nor to any other 



Science, except the Firfi; Philofophy. And therefore Sir Ifaac, in 



beginning his Syftem of Aftronomy with this propofition, has gone 



out of the limits of his Science, as much as Euclid would have done, 



if he had begun his Elements with the definition of Quantity, of 



Body, or of Magnitude. I do not, however, blame Sir Ifaac for 



this, as I hold the principles of all fciences to be founded in Meta- 



phyfics, or the Firfl Philofophy ; but, on the contrary, I commend 



him for laying the foundations of his Science fo deep, and giving 



the reader fo much information, which he certainly was not obliged 



to give him, — if the propofition be true. 



In examining the truth of it, I will begin with confidering the 



nature of Motion, which is the fubjedt of it. For this purpofe, I do 



not think it is neceflary to have recourfe to Ideas of fo high ab- 



flradion, as Poiver and Energy, by which Ariftotle has defined 



Motion t ; but it will be fufficient to mention that Quality of it, 



,, ,. -T which 



'f jf«i 1 



• Pages 246. and 251. The other paffage is in his Fourth Book, De Naturali 

 Ju/cultatitne, parag. 8. From which, and the Commentary of Simplicius upon it, 

 page 157, it is evident that he had no notion, either of the impulfe, after it had 

 ceafed, being the Caufe of the Motion of Projediles, or that the Motion continues 

 forever : The way he accounts for the continuation of it, fo long as it continues, is 

 from the Prefl"ure of the Air upon the Body in Motion, as I have explained at fome 

 length, page 246. 



f Vol. I. chap. 3.' 



