May or must?

In most situations you may is the most polite and you must the most rude.

Peter Farb, Word Play

Peter Farb

After making the statement above in his book Word Play, Peter Farb goes on to explain how the two phrases you may and you must can be confusing to those for whom English is a second language. As he says, in most situations the first usage is more polite than the second. But if that is true "in most situations," it means there are exceptions.

As a general rule, most of us prefer hearing the word may rather than must. The latter sounds like an order, while the former gives us permission. We like having a choice. It sounds like a kindness, while must sounds severe. Even when we were children, "you may go outside and play" sounded much better than "you must go outside and play." Even if we wanted to go outside and play, we didn't want to be ordered to do so. It took away some of the fun.

Yet as Farb suggests, there are exceptions to this rule. The example he gives is when a hostess at a dinner party passes her special dish to a guest and says, "You must try some of this." Is that an order? No, it is more of a recommendation. It means she thinks the dish is outstanding. If she had said, "You may try some of this," a person who grew up speaking English could think there was something questionable about it. They may like it or they may not. If you are finicky eater, you may very well pass on that dish.

Or suppose a friend tells you, "You must be crazy." This is neither an order nor a suggestion. Rather it is a joke, and obviously so to anyone who grew up speaking English. The words "you may be crazy" somehow seem less light. Perhaps your friend actually thinks you're crazy.

If you are learning English as a second language, these exceptions to the rule must be confusing. Or is it, may be confusing?