Finding common ground

At the end of chapter III of his book about St. Thomas Aquinas, Chesterton takes one Thomist sentence and tries to convey its importance for modern apologetics. His argument reminds me somewhat of a book that I once read: 'Finding common ground'. The general point: when talking with people of other convictions, one has to speak the same language. Or, in Chesterton's words:

If there is one phrase that stands before history as typical of Thomas Aquinas, it is that phrase about his own argument: "It is not based on documents of faith, but on the reasons and statements of the philosophers themselves." Would that all Orthodox doctors in deliberation were as reasonable as Aquinas in anger! Would that all Christian apologists would remember that maxim; and write it up in large letters on the wall, before they nail any theses there. At the top of his fury, Thomas Aquinas understands, what so many defenders of orthodoxy will not understand. It is no good to tell an atheist that he is an atheist; or to charge a denier of immortality with the infamy of denying it; or to imagine that one can force an opponent to admit he is wrong, by proving that he is wrong on somebody else's principles, but not on his own. After the great example of St. Thomas, the principle stands, or ought always to have stood established; that we must either not argue with a man at all, or we must argue on his grounds and not ours.