Chap. II. A N T 1 E N T METAPHYSICS, 335 



The propofitiou is thus exprefled by Sir Ifaac : * Corpus omnc 

 ' perfcvcrat in ftatu fuo quiefcendi vel movendi uniformiter in di- 



* redlum, nifi quatenus a yiribus impreffis cogitur (latum ilium mu- 

 ' tare.' The propofition, thus exprefled, I believe, would be hardly 

 vmderftood by an antient Roman * ; but, to us, who are accuftomcd 

 to the modern philofophical Latin, very different from that of Ci- 

 cero, it is intelligible enough, and may be thus rendered into Eng- 

 lifh : ' All Bodies perfevcre in their fl:ate, whether of Reft, or of 



* Motion uniformly in a ftraight line, unlcfs in fo far as, by fome 

 ' force imprefled upon them, they are obliged to change that ftate.' 



This propofition, which Sir Ifaac calls an Axiom, and lays down 

 as the foundation of his whole Syftem, aflerts, that Body, once put in 

 Motion by the impulfe of another Body, (for fo I underftand the 

 Axiom, for the reafon given in the preceding Chapter), will con- 

 tinue always to be moved in a ftraight line till its Motion be flop- 

 ped, or altered, by fomething foreign or extrinfic to it. And in this 

 refpeft Reft and Motion are faid by Sir Ifaac to be governed by the 

 fame law ; for he fays, as the Body continues at Reft till it be mo- 

 ved by fomething extrinfic to it, fo it alfo continues in Motion till it 

 be ftopped in the fame way. 



And here it muft, at firft fight, appear very extraordinary, that 

 an Axiom, fuch as this is faid to be, (that is, a Propofition, the truth 

 of which is immediately acknowledged by every man of common 

 fenfe, though uninftrudted in any art or fcience), fliould not have 

 been known to any of the antients. It is, I think, degrading the 

 antients lower than hitherto they have been degraded by the great- 

 eft vanity of modern times, to fuppofe that they were ignorant even 

 of Axioms and Firft Principles. Now that the antients knew no- 

 thing 



• See what I have faid concerning the language of this PropofrtioD, Vol. i. 

 page 530. 



