42 SOME REMARKS ON THE 



mind: and a distinction, analogous or identical with that be- 

 tween primary and secondary qualities, has accordingly been 

 expressed by the antithesis between that which is a parte 

 hominis and that which is a parte universi. That the dis- 

 tinction between primary and secondary qualities is necessary 

 on the hypothesis on which we are proceeding, appears at once 

 from the consideration that if we affirm that all the qualities 

 of bodies of which we can form any conception are equally 

 subjective and phenomenal, nothing will remain of which the 

 mind can take cognisance, and by means of which our con- 

 ception of the nature of any one substance can be discriminated 

 from that of any other*. Let it be granted therefore that the 

 distinction of primary and secondary qualities is a necessary 

 element of physical science. It follows from this that the 

 secondary qualities in a manner disappear when we look at 

 the universe from the scientific point of view. Instead of 

 colours we have vibrations of the luminiferous ether instead of 

 sounds vibrations of the ambient air, and so on. Now from 

 hence it follows that all the phenomena which we. see produced, 

 of whatever nature they may be, are all in reality dependent on 

 the primary qualities of matter. Furthermore, these primary 

 qualities themselves all involve the idea of motion or of a ten- 

 dency to motion. A body changes its form in virtue of tlxe 

 local motion (absolute or relative) of some of its parts; 'and 

 when I press a stone between my hands, I find that I can 

 produce no sensible change of form, while contrariwise the 

 stone reacts against my hands, tending to make them move in 

 opposite directions. I then say that the stone is hard as a 

 mode of expressing this, viz. that when an attempt is made to 

 produce relative local motion of its parts, it resists it in virtue 

 of its reactive tendency to produce motion in that which acts 

 upon it. Again, a body whose parts are readily susceptible of 

 relative local motion is said to be soft or fluid, and when a 

 sensible change of form is accompanied by a tendency to such 

 motion as shall restore the original form, it is said to be elastic, 

 and so on. We thus arrive at a point of view at which all 



* The doctrine of the cognoscibility of substantial forms, which is intimately 

 connected with this distinction, is, as Leibnitz in effect remarks, as it were the 

 common character of those who with more or less success attempted in the seven- 

 teenth century, the restoration of science. Vid. Leibnitz, Epist. ad Thomas, i. 



