My library book is due today, but I haven’t finished it yet. I can’t renew it because the library put it on hold for someone else. I’m willing to pay the penalty of 25 cents a day so I can keep reading. May I do that, or must I return the book? —Rachel, Salem, Oregon

YOU MUST return the book on time. That 25-cent charge isn’t a rental fee but an incentive to return the book promptly. The fact that the fee isn’t high enough to provide a proper incentive—say, $25 a day—doesn’t give you the freedom to hang on to a popular book past its due date. Similarly, the ability to pay a speeding ticket doesn’t make it OK to speed. The public library is a great institution. You should honor the intent of the 25-cents-a-day fine rather than embrace some sort of money-talks philosophy.

UPDATE: Rachel returned the book on time; she’ll check it out again.

—Adapted from ‘The Ethicist’ in The New York Times Magazine