But it is not sufficient to study the different parts of a cathedral in chronological order. It would be a dull biography of a man, and a dull history of a people, which put events correctly in chronological order, but did not point out the causal connection between them. It is just when we reach this point that the real interest begins. It does not interest one much to hear that an acquaintance whom we saw in London in the spring is now in the Australian bush: it does interest one when one hears that he had to leave the country because three months ago he was detected cheating at cards. So, in a cathedral, it is not enough to know that such a vault was put up or such a row of windows inserted in the fifteenth century. We want to know why the cathedral people constructed the vault or the windows just then; also, why they were not satisfied with what was there before; also, what was there before. And with the latter query comes in a fine field of action for what I believe is called the “constructive imagination.” On the motives which influenced mediæval builders I have laid considerable stress throughout the book, simply because, if it has occurred at all to writers to ask why such and such a change was made, the answer usually has been—I quote from an article on one of the cathedrals—“simply a desire for what was thought a far superior kind of beauty led to the alteration of this work”: _i.e._, the Gothic builders were æsthetic dilettanti, striving after prettiness for prettiness’ sake; on a level with painters and poets and musicians. Now, some changes were due, I admit, to æsthetic considerations simply: _e.g._, the substitution of the present choir for the former Transitional choir at York; so also one of every pair of towers at the west end of a cathedral; and every spire in the country. [Illustration: SOUTHWELL CHAPTER-HOUSE.] But the more the history of the cathedrals is studied, the more clearly it will be seen that the great majority of the alterations in the structure were forced on the ecclesiastical authorities of the day by practical considerations. The monastery was large, as at Canterbury, and the church the seat of an archbishop; Lanfranc’s short choir had to be replaced by a longer one.