Sentence:  ... this untoward Method allows him who is the "Respondent", to prevaricate from his Duty, and turn <WSD>"Opponent</WSD>:" Which "confounds" those two Offices, and "perverts" all the Laws of Reasoning or Discoursing. 
Meaning of the word marked with <WSD> tags:  The participant who opens an academic debate by putting forward objections to a theological or philosophical thesis.