52702
Though frequently absent due to his participation in the American Revolution , John Adams maintained a correspondence with his son , encouraging him to read works by authors such as Thucydides and Hugo Grotius .
 John Adams, Thucydides, Hugo Grotius
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 John Adams, Thucydides, Hugo Grotius