ARISTOTELIAN PHYSICS. 89 



"We seek," he says, 11 "the principles of sensible things, that is, ot 

 tangible bodies. We must take, therefore, not all the contrarieties of 

 quality, but those only which have reference to the touch. Thus black 

 and white, sweet and bitter, do not differ as tangible qualities, and 

 therefore must be rejected from our consideration. 



"Now the contrarieties of quality which refer to the touch are 

 these : hot, cold ; dry, wet ; heavy, light ; hard, soft ; unctuous, 

 meagre ; rough, smooth ; dense, rare." He then proceeds to reject 

 all but the four first of these, for various reasons ; heavy and light, 

 because they are not active and passive qualities ; the others, because 

 thev are combinations of the four first, which therefore he infers to be 

 the four elementary qualities. 



" 12 Now in four things there are six combinations of two ; but the 

 combinations of two opposites, as hot and cold, must be rejected ; we 

 have, therefore, four elementary combinations, which agree with the 

 four apparently elementary bodies. Fire is hot and dry ; air is hot 

 and wet (for steam is air) ; water is cold and wet, earth is cold and 

 dry." 



It may be remarked that this disposition to assume that some com- 

 mon elementary quality must exist in the cases in which we habitually 

 apply a common adjective, as it began before the reign of the Aristo- 

 telian philosophy, so also survived its influence. Not to mention other 

 cases, it would be difficult to free Bacon's Inquisitio in naturam calidi, 

 " Examination of the nature of heat," from the charge of confounding 

 together very different classes of phenomena under the cover of the 

 word hot. 



The correction of these opinions concerning the elementary com- 

 position of bodies belongs to an advanced period in the history of 

 physical knowledge, even after the revival of its progress. But there 

 are some of the Aristotelian doctrines which particularly deserve our 

 attention, from the prominent share they had in the very first begin- 

 nings of that revival ; I mean the doctrines concerning motion. 



These are still founded upon the same mode of reasoning from adjec- 

 tives ; but in this case, the result follows, not only from the opposition 

 of the words, but also from the distinction of their being absolutely or 

 relatively true. "Former writers," says Aristotle, "have considered 

 heavy and light relatively only, taking cases, where both things have 

 weight, but one is lighter than the other; and they imagined that, in 



De Gen. et Corrupt, ii. 2. 1S Ib. iii. 3. 



