76 THE GREEK SCHOOL PHILOSOPHY. 



science whatever ; we must collect the facts, and the 

 things to which the facts happen, in each subject, 

 and provide as large a supply of these as possible." 

 He then proceeds to say that " we are not to look 

 at once at all this collected mass, but to consider 

 small and definite portions "..."And thus it is the 

 office of observation to supply principles in each 

 subject ; for instance, astronomical observation sup- 

 plies the principles of astronomical science. For 

 the phenomena being properly assumed, the astro- 

 nomical demonstrations were from these discovered. 

 And the same applies to every art and science. So 

 that if we take the facts (rd vTrdp^ovra) belonging 

 to each subject, it is our task to mark out clearly 

 the course of the demonstrations. For if in our 

 natural history (Kara T^V \GTopiav) we have omitted 

 nothing of the facts and properties which belong to 

 the subject, we shall learn what we can demonstrate 

 and what we cannot." 



These facts, TO. uTra/s^oi/ra, he, at other times, in- 

 cludes in the term sensation. Thus he says 12 , "It is 

 obvious that if any sensation is wanting, there must 

 be also some knowledge wanting which we are thus 

 prevented from having, since we arrive at know- 

 ledge either by induction or by demonstration. 

 Demonstration proceeds from universal proposi- 

 tions, induction from particulars. But we cannot 

 have universal theoretical propositions except from 

 induction ; and we cannot make inductions without 

 12 Anal. Post. i. 18. 



