We are apt to wonder now how people were ever so psychologically impious as to attempt to teach in a single group, by means of the same cut-and-dried phrases, minds at every different stage of growth and of receptiveness; hurling ready-made truths at the devoted heads of pupils like so many tons of explosive bombs shot down from aircraft upon massed enemy battalions! Grading, and the individual point of contact—which, after all, is just Aristotle’s time-honoured principle of “beginning from that which we know”—these we recognise to be of the first importance, and that whether we be University professors or Sunday school teachers. And so we are prepared to appreciate a fourteenth century scheme which is dominated by the principle of graded progress. We note that the souls which are not yet psychologically fit to begin the regular course of purgation are kept outside, in Antepurgatory, for a longer or shorter term of years, as each has need. The “Infants,” so to speak, are graded among themselves, and are not grouped with “Standard I.” Within the Gate, the seven terraces are arranged in an order corresponding (not, of course, to a psychological series that would be accepted as it stands to-day, but) to a very carefully-thought-out classification of the seven capital sins; and until the lesson of a given Terrace is completely mastered, there is no chance of moving up. When, on the other hand, the teaching in that particular grade has been thoroughly grasped and the pupil has nothing more to learn there, no power in heaven or earth—or anywhere else—can keep him back. In Dante’s School there are no mistakes in grading, and no wrong removes. We have spoken of the “atmosphere” of the _Purgatorio_ as one of “naturalness,” meaning by that, that it is an environment not calculated to hamper or restrict normal and spontaneous development. It is “natural” also in a more literal sense, in that the Poet has seen fit to depart from the almost invariable tradition of his predecessors (who place Purgatory underground, side by side with Hell, and make it scarcely distinguishable therefrom save in the matter of duration) and to furnish his penitents with an “open-air cure.”