288 PHYSICAL SCIENCE IN THE MIDDLE AGES. 



the four invented by Aristotle, and stated with 

 additional accuracy the rules of hypothetical syllo- 

 gisms. He also, not only collected much informa- 

 tion concerning animals, and natural events, which 

 Aristotle had omitted, but often differed with his 

 master; as, for instance, concerning the saltness 

 of the sea : this, which the Stagirite attributed to 

 the effect of the evaporation produced by the sun's 

 rays, was ascribed by Theophrastus to beds of salt 

 at the bottom. Porphyry 5 , who flourished in the 

 third century, wrote a book on the Predicables, 

 which was found to be so suitable a complement to 

 the Predicaments or Categories of Aristotle, that it 

 was usually prefixed to that treatise ; and the two 

 have been used as an elementary work together, up 

 to modern times. The Predicables are the five steps 

 which the gradations of generality and particularity 

 introduce ; genus, species, difference, individual, 

 accident ; the Categories are the ten heads under 

 which assertions or predications may be arranged ; 

 substance, quantity, relation, quality, place, time, 

 position, habit, action, passion. 



At a later period, the Aristotelian commentators 

 became more servile, and followed the author step 

 by step, explaining, according to their views, his 

 expressions and doctrines; often, indeed, with ex- 

 treme prolixity, expanding his clauses into sentences, 

 and his sentences into paragraphs. Alexander 

 Aphrodisiensis, who lived at the end of the second 



* Buhfe, Arist. i. 284. 



