On Thursday, the Yale College faculty voted a change in the rules for Credit/D/Fail that will solve a problem in the sciences and create many new ones in other parts of the University. Students will the biggest losers.

Under the new rules, students will no longer be able to use courses taken Credit/D/Fail to satisfy their distribution requirements. And professors, like me, who currently do not allow Credit/D/Fail in their courses will no longer have that right.

The new system is much like what Princeton had when I taught there 1989-93: Students could take any course they wanted Pass/Fail. The result? My economic history course at Princeton consisted of two clearly different groups. About half the students — who were taking the course for a grade — worked hard and said they learned a great deal. The other half did almost nothing, knowing that an “F” then was as implausible as a “D” is at Yale today. Every year at the final exam I would meet students I had no recollection of ever seeing in lecture. At the end of every semester I would read term papers that would embarrass many high school students.

Scientists at Yale have been angry that students flock to the small number of science courses intended for non-majors, take them Credit/D/Fail, and then spoil the class for the few who are genuinely interested. I know this problem well: Serious Princeton students complained bitterly about the “ghosts” who got in the way of those who really wanted to learn. They asked, for good reason, why their institution would force them to put up with people who had no interest in the course material.

Seminars are not exempt. I wonder how many students will actually do the reading when they know that not doing any reading, but writing a mediocre term paper, will ensure a “Cr.” Foreign language courses are not exempt. Professors in those departments naturally wonder how many students will figure out the niceties of the pluperfect subjunctive when they will get a “Cr” in any case. The core courses in departments like economics are not exempt. I do not know what my department will do, but my hunch is that we will develop a system where non-majors and majors take the same courses, but only non-majors can take them Credit/D/Fail.

The new rules are also a bit cynical. The official reason for Credit/D/Fail is that students should be encouraged to experiment by taking courses they would not otherwise take for fear of a bad grade. That sounds great, but the evidence suggests other motivations. I’ve been asking students for years why they take courses Credit/D/Fail, and not one has said anything about experimentation. The explanation always has something to do with excess work: They are taking six courses, they are doing a play or a varsity sport. In other words, the purpose of Credit/D/Fail in reality is to let students treat four of their 36 Yale credits as a joke. If students are too busy to do 36 credits, it would be better to consider ways to reduce the workload, rather than encourage the view that they should do too much, and some of it badly.

I have always enjoyed my Yale courses more than I did teaching at Princeton. And no, it’s not because Yalies are smarter than Princetonians. Until now, I could expect that everyone who took my course at Yale was serious about it. That allowed me to challenge students, and give them the pleasure of learning that they could meet that challenge. Yale just took that away from all of us.

The loser in Thursday’s decision is undergraduate education at Yale.

Timothy Guinnane is a professor of economics and history.