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The term came into its modern philosophical usage through Immanuel Kant , who contrasted it with the noumenon , which " cannot " be directly observed .
 Immanuel Kant
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:
 Immanuel Kant