Fig. to put forward arguments against or objections to a proposition-which one may actually agree with-purely to test the validity of the proposition. (The devil's advocate opposes the canonization of a saint in order to prove that the grounds for canonization are sound.) I agree with your plan. I'm just playing the devil's advocate so you'll know what the opposition will say. Mary offered to play devil's advocate and argue against our case so that we would find out any flaws in it.