I recently handed in my grades for an undergraduate course I teach at Duke University. They were a very limited assortment: A, A-minus, B-plus, B and B-minus. There were no C's of any flavor and certainly no D's or F's. It was a good class, but even when classes aren't very good, I just drop down slightly, to grades that range from A-minus to B-minus.

The last time I gave a C was more than two years ago. That was about the time I came to realize that my grading had become anachronistic. The C, once commonly accepted, is now the equivalent of the mark of Cain on a college transcript. I have forsworn C's ever since.

How rare is the C in college? The data indicate that not only is C an endangered species but that B, once the most popular grade at universities and colleges, has been supplanted by the former symbol of perfection, the A.

For example, at Duke, which all evidence indicates is not a "leader" in grade inflation -- by a long shot -- C's now make up less than 10 percent of all grades. In 1969 the C was a respectable thing, given more than one-quarter of the time. A's overcame B's to reach the top of the charts in grade popularity in the early 1990s.

At Pomona College, C's are now less than 4 percent of all grades. About half of all grades at Pomona, Duke, Harvard and Columbia are in the A range. State schools are not immune to this change. At the University of Illinois, A's constitute more than 40 percent of all grades and outnumber C's by almost three to one. (More information on this subject can be found at www.gradeinflation.com.)

This trend of the dominance of the A and the diminution of the C began in the 1960s, abated somewhat in the '70s and came back strong in the '80s. The previous signs of academic disaster, D and F, went by the wayside in the Vietnam era, when flunking out meant becoming eligible for the draft. At Duke, Pomona, Harvard and elsewhere, D's and F's combined now represent about 2 percent of all grades given.

A perusal of grade inflation rates at those few institutions open enough to publish such information indicates that, on average, grade-point averages are rising at a rate of about 0.15 points every decade. If things go on at that rate, practically everybody on campus will be getting all A's before mid-century, except for the occasional self-destructive student who doesn't hand in assignments or take exams -- if exams are even given.

A's are common as dirt in universities nowadays because it's almost impossible for a professor to grade honestly. If I sprinkle my classroom with the C's some students deserve, my class will suffer from declining enrollments in future years. In the marketplace mentality of higher education, low enrollments are taken as a sign of poor-quality instruction. I don't have any interest in being known as a failure.

Parents and students want high grades. Given that students are consumers of an educational product for which they pay dearly, I am expected to cater to their desires not just to be educated well but to receive a positive reward for their enrollment. So I don't give C's anymore, and neither do most of my colleagues. And I can easily imagine a time when I'll say the same thing about B's.

University leaders, like stock market analysts talking about the Internet bubble not so long ago, sometimes come up with ridiculous reasons to explain grade inflation. We are teaching more effectively, some leaders say, or students are smarter and better than in previous decades. Many students and parents believe these explanations. They accept the false flattery as the real thing. Unlike high-tech stock prices, the grade inflation bubble, I'd guess, will not burst.

As grades spiral upward, my job becomes more difficult. Somehow, I have to get the most from my students without the external motivator of grades. True, for some students -- those with a strong internal desire to learn -- the absence of real grades is actually a blessing. Outstanding students don't need a teacher who carries a big stick. They need educators who are partners and facilitators in learning.

But not every student is so motivated. So when the commonest grade is A, I have to use other means to get them to learn: I have to cajole, to gently persuade. And in all honesty, I don't think I have the psychological skills necessary in this climate to approach my goal of educating all my students well. Many of my colleagues around the country would, I think, acknowledge a similar lack of such skills if pressed.

Today's classes, as a result, suffer from high absenteeism and a low level of student participation. In the absence of fair grading, our success in providing this country with a truly educated public is diminished. The implications of such failure for a free society are tremendous.

The writer is a professor at Duke University and a visiting scholar at Stanford University.