On old books, back to Screwtape, letter 27, para. 5:
Only the learned read old books and we have now so dealt with the learned that they are of all men the least likely to acquire wisdom by doing so. We have done this by inculcating the Historical Point of View. The Historical Point of View, put briefly, means that when a learned man is presented with any statement in an ancient author, the one question he never asks is whether it is true.
By Lewis’s standards, books from the 17th-18th centuries, written in English, probably don’t even qualify as old books–but they’re definitely older than most of what I read, and we’re certainly reading them to address the truth of the content (and with a presumption in favor of their truth).
But I suspect the discussion I was really thinking of was in God in the Dock, Part II, Ch. 4, “On the reading of old books,” pages 200-207 of my copy. Some relevant quotes:
. . . I do not wish the ordinary reader to read no modern books. But if he must read only the new or only the old, I would advise him to read the old.
It is a good rule, after reading a new book, never to allow yourself another new one till you have read an old one in between. If that is too much for you, you should at least read one old one to every three new ones.
We may be sure that the characteristic blindness of the twentieth century – the blindness about which posterity will ask, ‘But how could they have thought that?’ – lies where we have never syspected it, and concerns something about which there is untroubled agreement between Hitler and President Roosevelt or between Mr. H. G. Wells and Karl Barth. None of us can fully escape this blindness, but we shall certainly increase it, and weaken our guard against it, if we read only modern books.
To be sure, the books of the future would be just as good a corrective as the books of the past, but unfortunately we cannot get at them.
And he does cite a number of 17th-century authors among the “old books”, so I guess I can feel comfortable on that question.