We must follow, then, the clue(20) of our discussion, meeting every effort of our opponents with reciprocal vigor. I say that my Gospel is the true one; Marcion, that his is. I affirm that Marcion's Gospel is adulterated; Marcion, that mine is. Now what is to settle the point for us, except it be that principle(1) of time, which rules that the authority lies with that which shall be found to be more ancient; and assumes as an elemental truth, (2) that corruption (of doctrine) belongs to the side which shall be convicted of comparative lateness in its origin.