We can agree a priori, however, with the remark of Schopenhauer that “the safest way to have no thoughts of one’s own is to take up a book every moment one has nothing else to do.” And we may agree with him further: “A man should read only when his thoughts stagnate at their source, which will happen often enough even with the best of minds. On the other hand, to take up a book for the purpose of scaring away one’s own original thoughts is a sin against the Holy Spirit. It is like running away from Nature to look at a museum of dried plants, or gaze at a landscape in copper-plate.”[16] It would be folly to lay down any fixed mathematical ratio between the time we should devote to reading and the time we should give to thinking. But one hour given to reading plus one hour given to thinking would be certainly more beneficial than two hours devoted entirely to reading. You can find quite a number of serious-minded men who put by a certain period each day for reading. But how many of them put by any time at all for thinking? It would be unjust to say they do not think. But at best their thinking is merely accidental—and apparently considered so. Surely it is as important that we lay aside a definite period each day for thinking as it is that we lay aside some time for reading. But how much this time should be and whether it should bear any specific ratio to the time given to reading can best be decided after a consideration of the problem of how to read. This problem has unfortunately been much misconceived. Those who have laid stress on the maxim, “A good book should be read over and over again,” have done so in the belief that this is the best way to get the most out of a particular book. But the object of reading is not to get the best out of any one book, but out of reading in general. A realization of this end will change our problem somewhat. It will bring us to a consideration, for example, of the law of diminishing returns. While the more we re-read a book the more we get out of it, it must be remembered that with a few possible exceptions, every time we re-read it we add less to our knowledge than we did the previous time. This means that we can usually make much faster progress by reading other books, in which case we do not merely read over what we already know for the most part. Whether re-reading is ever justified, and when, is a question which will be considered a little later. The law of diminishing returns applies to an entire subject as well as to a single book. That is to say, past a certain point, every book we read on a particular subject, while it will probably add to our knowledge, will not yield as much return as a book of equal merit on another subject, new to us.