394 NEW ESSAYS 



modifications of one and the same thing, as our author 

 said in the passage I have quoted from his first letter 149 . 

 We must certainly distinguish between modifications 

 and attributes. The faculty of having perception and 

 that of acting, extension, and solidity are attributes or 

 perpetual and principal predicates ; but thinking, impetus 

 [impetuosity], figures and motions are modifications of 

 these attributes 15 . Further, we ought to distinguish be- 

 tween physical (or rather_real) genus and logical or ideal 

 serins. Things which are of the same physical genus, 

 or which are homogeneous, are of the same matter, so to 

 speak, and can often be changed one into another by 

 changing their modification, like circles and squares. 

 But two heterogeneous things may have a common logical 

 genus, and then their differences are not mere accidental 

 modifications of one and the same subject [swje] m , or 

 one and the same matter, metaphysical or physical. Thus 

 time and space are very heterogeneous things, and it would 

 be a mistake to suppose I know not what real common 

 ground [sujet], having nothing but continuous quantity 

 in general, from the modifications of which time and 

 space arise. Nevertheless their common logical genus is 

 continuous quantity 152 . Some one will perhaps ridicule 

 this distinction 153 of the philosophers between two genera, 

 the one merely logical, the other real 154 , and between 

 two matters, the one physical (that of bodies), the other 

 merely metaphysical or general, as if one were to say 

 that two parts of space have the same matter, or that 

 two hours also have each the same matter as the other. 

 Yet these distinctions are distinctions not only of terms 

 but of things themselves, and they appear to be most 



ia Supra, p. 392. 



150 Cf. Introduction, Part ii. p. 34 ; Part iii. p. 127 ; Monadology, 

 14 sqq. 



151 Q r < ground.' 152 E. gives this sentence ; G. omits it. 

 153 E. reads ' these distinctions.' 



184 E. reads ' also real.' 



