THE PHILOSOPHICAL WORKS. 29 



butes 1 , or in other words it is the formal cause of the qualities 

 which are referred to it. As there is a difference between the 

 properties of different substances, there must be a corresponding 

 difference between the substances themselves. But in the first 

 state of the views of which we are speaking this latter differ- 

 ence is altogether unimaginable : " distincte quidem intelligi 

 potest, sed non explicari imaginabiliter." 2 It belongs not to 

 natural philosophy, but to metaphysics. 



These views however admit of an essential modification. If ^ 

 we divide the qualities of bodies into two classes, and ascribe 

 those of the former class to substance as its essential attributes, 

 while we look on those of the latter as connected with substance 

 by the relation of cause and effect that is, if we recognise the 

 distinction of primary and secondary qualities the state of the 

 question is changed. It now becomes possible to give a definite 

 answer to the question, Wherein does the difference between 

 different substances, corresponding to the difference between 

 their sensible qualities, consist? 



The answer to this question of course involves a reference 

 to the qualities which have been recognised as primary; and we 

 are thus led to the principle that in the sciences which relate to 

 the secondary qualities of bodies the primary ones are to be 

 regarded as the causes of the secondary. 3 



This division of the qualities of bodies into two classes is the 

 point of transition from the metaphysical view from wHich we 

 set out to that of ordinary physical science. And this tran- 

 sition Bacon had made, though not perhaps with a perfect con- 

 sciousness of having done so. Thus he has repeatedly denied the 

 truth of the scholastic doctrine that Forms are incognoscible 

 because supra-sensible 4 ; and the reason of this is clearly that his 

 conception of the nature of Forms relates merely to the primary 

 qualities of bodies. For instance, the Form of heat is a kind of 

 local motion of the particles of which bodies are composed 5 , and 

 that of whiteness a mode of arrangement among those particles. 6 

 This peculiar motion or arrangement corresponds to and en- 

 genders heat or whiteness, and this in every case in which those 

 qualities exist. The statement of the distinguishing character 



1 See Zimmerman's Essay on the Monadology of Leibnitz, p. 86. (Vienna, 1807). 



2 Leibnitz, De ipsii Natura. 8 Whewell, Phil. Ind. Science, [book iv. ch. i.J 



4 See Scaliger, Exercit. in Cardan. 



5 [Nov. Org. ii. 20.] 6 [Valerius Terminus, ii. 1.] 



