34S ANTIENT METAPHYSICS. Book IV. 



and future, apply to it. It therefore belongs to this univerfal philo- 

 fophy to treat of it. 



If there were no motion^ fays Euclid, there would be no found, nor 

 any fenfe of hearing* — He might have added, nor any other perception 

 of fenfc — Further, there would have been no vifible world, nor gene- 

 ration or produdion of any kind here below — and, among other 

 things, time could have had no exiftence. And this ftill further fhews 

 us the necefTity of knov^^ing what motion is, upon which fo many 

 things depend, and without the knowledge of which it is impoffible to 

 underftand either phyfics or metaphyfics. 



Time is like motion, and many other things, which every body 

 thinks he knows, and, indeed, has fome notion of it, but very few 

 perfedly underftand. ' If no body afk me what time is,' fays St Au- 

 guftine, * I think I know ; but, if any body afk me, I cannot tell.* 

 And, indeed, it is not eafy to give a clear idea of time at once ; but, in 

 the following manner, I think, the definition of it may be inveftigated, 

 and brought out by degrees, beginning with the mofl: general of all 

 ideas, exijlence. 



If nothing exifted, it is evident there could be no fuch thing as 

 time. 



Further, if there were no continuation of exiftence, there could be 

 no time^ becaufe there would be nothing to which it could be ap- 

 plied. This continuation of exiftence is what is called duration. 



Further, ftill, as time is acknowledged by every body to be a mea^ 

 fure of fomething ; and, as we can conceive it applied to nothing but 

 duration^ (for it cannot be applied to quantity, that is, to magnitude 



and 



• Euclid, fcUio Canonis in initio^ 



