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In modern philosophy , René Descartes ' famous inquiry into mind and body began as an exercise in skepticism , in which he started by trying to doubt all purported cases of knowledge in order to search for something that was known with absolute certainty .
 René Descartes
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 René Descartes