It is a widely held misconception that Feynman's undergraduate course was a failure, and that The Feynman Lectures on Physics (FLP) is  not useful as a textbook for beginners. FLP was used very successfully to teach introductory physics for almost 20 years at Caltech (accompanied by exercise books that were originally published by Addison-Wesley, and later self-published by Caltech). FLP has also been translated into over a dozen languages, and is used in the classroom more often in translation than in the original English. [For example, FLP and its exercise books are very popular in the former Soviet States— it is believed that millions more copies have been printed in Russian than in English, though the exact number is unknown.]

Feynman himself is partly to blame for the misconception that his course was a failure, as this is largely due to comments he made in an AIP interview with Charles Weiner in 1966, in which he basically reiterated his self-deprecating preface in FLP, which was later repeated by David Goodstein (host of "The Mechanical Universe") and Gerry Neugebauer in their preface to The Commemorative Issue of FLP, published 10 years after Feynman's death. However, in the same interview (which spanned several days) Feynman told Weiner that "People who were directly in contact [with the students] would tell me that I was underestimating them, and that it wasn't as bad as I thought.", and that he had "better feelings" about FLP since writing his preface. Years later, in interviews with Mehra, Feynman said that creating FLP was one of the best things he did. So, his feelings about FLP seem to have improved with age.

Matthew Sands, one of the three authors of FLP, is arguably the person most responsible for it's creation. It was Dr. Sands who had the idea of modernizing the core undergraduate physics course at Caltech, and it was also his idea to have Feynman teach the course. About Feynman's FLP preface, Sands writes the following:

"After the completion of the second year of lectures—near the beginning of June, 1963—I was in my office assigning the grades for the final examinations, when Feynman dropped in to say goodbye before leaving town (perhaps to go to Brazil). He asked how the students had performed on the exam. I said I thought pretty well. He asked what was the average grade, and I told him—something like 65 percent as I recall. His response was, "Oh, that’s terrible, they should have done better than that. I am a failure." I tried to dissuade him of this idea, pointing out that the average grade was very arbitrary, depending on many factors such as the difficulty of the problems given, the grading method used, and such—and that we usually tried to make the average sufficiently low that there would be some spread in grades to provide a reasonable "curve" for the assignment of letter grades. (This is an attitude, incidentally, that I wouldn't approve of today.) I said that I thought that many of the students had clearly got a great deal out of the class. He was not persuaded.

I then told him that the publication of the lectures was proceeding apace and wondered whether he would like to provide some kind of preface. The idea was interesting to him, but he was short of time. I suggested that I could turn on the dictating machine I had on my desk, and that he could dictate his preface. So, still thinking about his depression over the average grade on the final exam of the second year students, he dictated the first draft of "Feynman's Preface", which you will find in front of each volume of the Lectures. In it he says: "I don’t think I did very well by the students." I have often regretted that I had arranged for him to make a preface in this way, because I do not think that this was a very considered judgment. And I fear that it has been used by many teachers as an excuse for not trying out the Lectures with their students." ¹

About David Goodstein's preface to The Commemorative Issue of FLP, Sands writes,

"In a Special Preface to the Commemorative Issue of the Feynman Lectures on Physics, David Goodstein and Gerry Neugebauer have written that "… as the course wore on, attendance by the registered students started dropping alarmingly."  I don't know where they got this information. And I wonder what evidence they have that:  "Many of the students dreaded the class..."  Goodstein was not at Caltech at that time.  Neugebauer was part of the crew working on the course, and would sometimes jokingly say that there were no undergraduate students left in the lecture hall—only grad students.  That may have colored his memory.  I was sitting at the back of the hall at most of the lectures, and my memory—of course, dimmed by the years—is that perhaps twenty percent or so of the students were not bothering to attend. Such a number would not be unusual for a large lecture class, and I do not remember that anyone was "alarmed".  And although there may have been some students in my recitation section who dreaded the class, most were involved and excited by the lectures—although some of them, very likely, would have dreaded the homework assignments." ¹

As further evidence against this common misconception please see the following photograph of a typical Feynman Lecture classroom. Look at the faces—they are all very young, except a small minority in the back. (Those with ties are professors.)

Feynman Lectures Classroom

Finally, here's what Feynman said to Mehra in a January 1988 interview (only about a month before Feynman died; these, I believe, are Feynman's last recorded words regarding FLP):

"At the end of the two years [1961-63] I felt that I had wasted two years, that I had done no research during this entire period and I was muttering to this effect. I remember Robert Walker saying to me: "Someday you will realize that what you did for physics in those two years is far more important than any research you could have done during the same period." I said, "You're crazy!" I don't think he's crazy now. I think he was right. The books [Feynman Lectures on Physics] are popular, they are read by a lot of people, and when I read them over [I find] they're good, they're all right. I am satisfied; rather, I am not dissatisfied with them. I am just dissatisfied with the system—whether it would transmit. But when you have a book and somebody from far away writes that he is learning from it... then I feel that I may have done something to a large number of other people, to people everywhere.

They have the books on the shelves. They are used all the time. They are twenty-five years old, and they are still on the shelves. Undergraduate and graduate students use them. They look them up for fundamental ideas behind advanced subjects. There is all kinds of stuff there, more basic physical points of view, and so apparently they are useful. I must admit now that I cannot deny that they are really a contribution to the physics world." ²

From what I have been able to gather in 10 years of working with FLP, the main reasons you do not see it used as a textbook very often are

(1) FLP lacks exercises and includes relatively few worked-out examples.

(2) Many  teachers are intimidated by Feynman's brilliance and style—it is hard to compete with Feynman, as a teacher.

My colleagues and I are currently addressing (1) by creating a new edition of FLP that will include a fourth volume with about 1000 exercises from the original Feynman Lectures course at Caltech, complete with answers, and some full solutions provided as examples.

As for (2), we hope to eventually address this problem by creating a "teacher's guide" for FLP that includes worked out solutions for all the exercises in the fourth volume, test problems and their solutions, but perhaps more  importantly, descriptions of classroom demonstrations that can be used to show students the physical significance of the material covered in FLP, and worked-out applications that show how the material can be used to solve real-world problems.

Michael A. Gottlieb   (April 19,2010)
Editor, The Feynman Lectures on Physics, Definitive Edition
Coauthor (with Feynman and Ralph Leighton), Feynman's Tips on Physics, a problem-solving supplement to The Feynman Lectures on Physics
—
Physics Department
The California Institute of Technology

1. 'On the Origins of The Feynman Lectures on Physics, A memoir by Matthew Sands,' Feynman's Tips on Physics (2006)
2.  The Beat of a Different Drum, by Jagdish Mehra, 1994 (by far my favorite Feynman biography)