The Greeks 19 



Plato divides the objects of our experience into four progressive 

 stages of which the two lower deal with the phenomena of the 

 visible or sensible world and opinion, and the two higher with 

 the aspects of the intelligible world and knowledge. To each of 

 these classes of objects there is a corresponding stage in the de- 

 velopment of human intelligence : 



(i) Opinion or conjecture (tlKaata ), which has for its objects 

 images, such as shadows, and reflections from smooth bright 

 surfaces. 



(2) Belief (TTto-Tts), which deals with the objects which are the 

 originals of the images which resemble them, and which include 

 animals, everything that grows, and all kinds of workmanship. 



(3) Understanding ( Stavota), which has for its objects sym- 

 bols, diagrams, and models, and which proceeds from hypothesis 

 downward to conclusion, and logically involves the process of 

 deduction. 



(4) Pure Intelligence or Dialectic, which deals with the Ideas 

 or Forms themselves, which involves no sensuous representation, 

 and which proceeds from hypothesis upward to first principles 

 inductively by means of ideas alone. 



This classification of the dififerent stages involved in the method 

 of knowledge is further illustrated in the analogy of the Cave in 

 the seventh book of the " Republic," and its general nature is 

 emphasised throughout those of Plato's dialogues whose primary 

 interest is epistemological. 



Plato's historical significance in the philosophical interpreta- 

 tion of the method of experience lies first in the fact that in his 

 " Theory of Ideas " he involves the conception of a rational 

 universe whose ideas and forms can be realised through the 

 phenomena of common experience which partially conform to 

 the idea, and imperfectly embody the lav/ or method of universal 

 principles: a conception of the world which implicitly underlies 

 the later investigations of Bacon. Further, Plato analyses the 

 process of experience and seeks to determine the validity of sen- 

 sation and the limitations of knowledge, thus laying the basis for 

 the epistemological critique of experience which was to be the 

 work of Kant. 



