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One explanation for the existence of parties , advanced by John Aldrich , is that the existence of political parties means that a candidate in one electoral district has an incentive to assist a candidate in a different district , when those two candidates have a similar ideology .
 John Aldrich
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:
 John Aldrich