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The evolution of the Greek art seems to go parallel with the Greek philosophical conceptions , which changed from the natural-philosophy of Thales to the metaphysical theory of Pythagoras .
 Thales, Pythagoras
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Thales, Pythagoras