The following is from Mortimer J. Adler's How to Read a Book. It can be found on pp. 6-10 of the 1940 edition of the book; it is here cited from the 1965 edition, the entirety of which is available online by clicking the title of this post. You can also find the link through the Wikipedia page for 'How to Read a Book'.
I did not discover I could not read until after I had left college. I found it out only after I tried to teach others how to read. Most parents have probably made a similar discovery by trying to teach their youngsters. Paradoxically, as a result, the parents usually learn more about reading than their children. The reason is simple. They have to be more active about the business. Anyone who teaches anything has to.
To get back to my story. So far as the registrar's records were concerned, I was one of the satisfactory students in my day at Columbia. We passed courses with creditable marks. The game was easy enough, once you caught on to the tricks. If anyone had told us then that we did not know much or could not read very well, we would have been shocked. We were sure we could listen to lectures and read the books assigned in such a way we could answer examination questions neatly. That was the proof of our ability.
Some of us took one course which increased our self-satisfaction enormously. I had just been started by John Erskine. It ran for two years, was called General Honors, and was open to a select group of juniors and seniors. It consisted of nothing but "reading" the great books, from the Greek classics through the Latin and medieval masterpieces right down to the best books of yesterday, William James, Einstein, and Freud. The books were in all fields: they were histories and books of science or philosophy, dramatic poetry and novels. We discussed them with our teachers one night a week in informal, seminar fashion.
That course had two effects on me. For one thing, it made me think I had struck educational gold for the first time. Here was real stuff, handled in a real way, compared to the textbook and lecture courses that merely made demands on one's memory. But the trouble was I not only thought I had struck gold; I also thought that I owned the mine. Here were the great books. I knew how to read. The world was my oyster.
If, after graduation, I had gone into business or medicine or law, I would probably still be harboring the conceit that I knew how to read and was well read beyond the ordinary. Fortunately, something woke me form this dream. For every illusion that the classroom can nourish, there is a school of hard knocks to destroy it. A few years of practice awaken the lawyer and the doctor. Business or newspaper work disillusions the boy who thought he was a trader or a reporter when he finished the school of commerce or journalism. Well, I thought I was liberally educated, that I knew how to read, and had read a lot. The cure for that was teaching, and the punishment that precisely fitted my crime was to having to teach, the year after I graduated, in this very Honors course which had so inflated me.
As a student, I had read all the books I was now going to teach but, being very young and conscientious, I decided to read them again- you know, just to brush up each week for class. To my growing amazement, week after week, I discovered that the books were almost brand new to me. I seemed to be reading them for the first time, these books which I thought I had "mastered" thoroughly.
As time went on, I found out not only that I did not know very much about any of these books, but also that I did not know how to read them very well. To make up for my ignorance and incompetence I did what any young teacher might do who was afraid of both his students and his job. I used secondary sources, encyclopedias, commentaries, all sorts of books about books about these books. In that way, I thought, I would appear to know more than the students. They wouldn't be able to tell that my questions or points did not come from my better reading of the book they too were working on.
Fortunately for me I was found out, or else I might have been satisfied with getting by as a teaching just as I had got by as a student. If I had succeeded in fooling others, I might soon have deceived myself as well. My first good fortune was in having as a colleague in this teaching Mark Van Doren, the poet. He led off in the discussion of poetry, as I was supposed to do in the case of history, science, and philosophy. He was several years my senior, probably more honest than I, certainly a better reader. Forced to compare my performance with his, I simply could not fool myself. I had not found out what the books contained by reading them, but by reading about them.
My questions about a book were of the sort anyone could ask or answer without having read the book—anyone who had had recourse to the discussion which a hundred secondary sources provide for those who cannot or do not want to read. In contrast, his questions seemed to arise from the pages of the book itself. He actually seemed to have some intimacy with the author. Each book was a large world, infinitely rich for exploration, and woe to the student who answered questions as if, instead of traveling therein, he had been listening to a travelogue. The contrast was too plain, and too much for me. I was not allowed to forget that I did not know to read.
My second good fortune lay in the particular group of students who formed that first class. They were not long in catching on to me. They knew how to use the encyclopedia, or a commentary, or the editor's introduction which usually graces the publication of a classic, just as well as I did. One of them, who has since achieved fame as a critic, was particularly obstreperous. He took what seemed to me endless delight in discussing the various about the book, which could be obtained from secondary sources, always to show me and the rest of the class that the book itself still remained to be discussed. I do not mean that he or the other students could read the book better than I, or had done so. Clearly none of us, with the exception of Mr. Van Doren, was doing the job of reading.
After the first year of teaching, I had few illusions left about my literacy. Since then, I have been teaching students how to read books, six years at Columbia with Mark Van Doren and for the last ten years at the University of Chicago with President Robert M. Hutchins. In the course of years, I think I have gradually learned to read a little better. There is no longer any danger of self-deception, of supposing that I have become expert. Why? Because reading the same books year after year, I discover each time what I found out the first year I began to teach: the book I am rereading is almost new to me. For a while, each time I reread it, that I had really read it well at last, only to have the next reading show up my inadequacies and misinterpretations. After this happens several times, even the dullest of us is likely to learn that perfect reading lies at the end of the rainbow. Although practice makes perfect, in this art of reading as in any other, the long run needed to prove the maxim is longer than the allotted span.