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Both Peirce and Wittgenstein introduced the analogy of colour theory in order to illustrate the shades of meanings of words .
 Peirce, Wittgenstein
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Peirce, Wittgenstein