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Many scientific realists ( e.g. , Ernan McMullin , Richard Boyd ) think the operational success of a theory lends credence to the idea that its more unobservable aspects exist , because they were how the theory reasoned its predictions .
 Ernan McMullin, Richard Boyd
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Ernan McMullin, Richard Boyd