The first man, who says, “It is a living oak consonant in all its parts,” does not deny that the acorn is different from the mature tree: the young sapling different in form from either the original acorn or the tree as it now appears. He does not deny that in a hundred years the form of the tree will seem to have changed still more; that in the fifty years past it has changed. What he denies is that there has been any change in that by which an oak is an oak. It is essentially the thing which it has always been. That is his contention. Its growth is normal to its nature, and in so far as growth involves change, such change is the very proof of identity. His opponent denies this. He says it was an oak once, long ago, but other plants grafted on it have so changed its nature that it can be called an oak no longer. The appeal of the one is not to a supposed dead mechanical rigidity; it is not an affirmation that he has before him an acorn rather than an oak; it is to that principle of one-ness by which any thing is what it is. The appeal of his opponent is not to the mere fact of change (at least he must be very unintelligent if that process destroy in his eyes all essential unity in the developing thing); it is rather to the proposition that the changes were of a disfiguring and (to borrow a foreign word) “denaturing” kind. The one says, “Here is the same original organism, in full health and strength, growing and vigorous before our eyes.” The other says, “These changes, which I can substantiate by the consultation of old pictures and written records of the thing, are a proof of disease and of corruption.” It is therefore quite beside the mark for the opponents, upon historical grounds, of some particular institution essential to the Catholic Church--for instance, the Primacy of Peter--to prove by elaborate reference to record that the Papal power under St. Clement was embryonic compared with the Papal power under Innocent III. It is quite beside the mark to bring forward, at too much pains, evidence on, say, the doctrine of the Real Presence to prove that its definition in the Council of Trent is far more elaborate, exclusive and exact than the statement of it in Justin Martyr, fourteen hundred years earlier. The point is that the one party to the controversy regards such change--if you like to call it change--as an inevitable and salutary phenomenon of life and a very proof of unity in character and time: the other, as a phenomenon opposed to the true life of the thing and a proof of its loss of identity with its original principle of life. Now in my view there are two tests which one may apply to what I have called the Protestant argument from History: two tests by which one may discover that it rings false. And these I would tabulate as follows: (1) The test of Innovation. (2) The test of Critical Date.