One of the fine old weapons in the Etiquette Arsenal used to be the reprimand "There is a time and a place for that sort of thing."

The words "and this isn't it" were understood.

Delivered with something of a sniff (head tilted back, eyebrows slightly raised, nose pointed upward, features frozen except for a quivering of the nostrils and the minimum lip movement necessary to pronounce the words), this statement informed dependents that they had just demonstrated ignorance of a sense of the appropriate.

What was most crushing about this enjoinder was that it squashed any hope the perpetrator might have had of shocking the elders. The time-and-place remark made it clear that it was not the action itself that was being condemned but the arena in which it was performed.

Miss Manners wishes to reinstate this valuable tool. She finds she must give lessons in its use, because while the young naturally have no sense of context unless they are taught, present-day grown-ups have lost confidence in the notion that proper behavior is not always an absolute but may vary with the circumstances.

Let us say that a youngster pronounces an obscene word to his grandparents in the hope of amazing and terrifying them by introducing them to the concept of human sexuality, of which they had not been previously aware. When he has reason to believe that the desired result has been achieved (because they flinch), he then offers a defense based on the necessity of facing the true raw realism of life, or he delivers the news bulletin that the word is in use elsewhere.

No sensible grown-up should let him get away with this. The child has to be informed that what he has demonstrated is not worldliness, but the fact that he is stuck at a primitive level of knowledge about human society. Mastering the ability to judge social context is one of the more sophisticated achievements one needs before being considered civilized.

However, we live in naive times, and that childish defense is constantly being put forward, even by grown-ups, who ought to know better, to the stupefaction of other grown-ups, who ought to know how to disallow it.

One is always hearing violators of the simplest social conventions -- vocabulary, fit subject matter for conversation, clothing, the distinction between public and private behavior -- arguing that what they are doing is appropriate somewhere and therefore could not be inappropriate anywhere.

They will, for example, claim the right to use certain words or to discuss certain matters in the drawing room, on the public airways, in institutional computer systems or in any open forum, on the grounds that the words appear in good literature or the topics are the object of scientific inquiry.

Naively denying the symbolic function of clothing, they will point out that the outfits others try to call vulgar or scandalous are, in fact, proper attire in other places. If bathing suits, or near-nudity, are acceptable on the beach, why can't one appear thus in town? If sweat-clothes are proper for lounging, why are they improper at parties? If black dresses are suitable for parties, why aren't they acceptable at weddings?

Perhaps the violators of convention will reveal the fact that certain actions that are frowned upon when practiced in public are actually normal behavior. Revealing that it is natural for romantic couples to kiss, for example, or for a mother to breast-feed a child, is supposed to establish that it is therefore unnatural to object to being required to view these actions.

People who are frank about their desire to get ahead in their work argue that it is therefore unfair to expect them to refrain from trying to drum up business among people they meet at social gatherings.

All of this attempts to deny the importance of venue. The richness of civilized society depends on the ability to understand the subtleties of context, to manage more than one style of behavior and to have a high sense of occasion.

Knowing how to behave is only part of the struggle. One must also know when and where.

Q: Does your rich and worldly experience include a notion of the protocol of skinny-dipping? Are my friends whose traditions include repairing to the old swimming hole obligated to warn their guests of the impending peer pressure to peel?

I have found myself straining to appear credible in asserting that, yes, I drove four hours up here to the mountains, and, yes, it is 90 degrees outside, but, no, I'm just not in the mood for a swim. When a mild-mannered citizen arrives at such a party to find nothing resembling a cabana to change in, when he or she is then forced to examine other guests from all conceivable angles, when all conversation ends with "We'd like to see more of you," is the fault with the host or the guest's expectations?

A: The host. Hosts always have an obligation to alert people ahead of time about what dress is expected.

Miss Manners hopes you don't think that she limits her worldly knowledge to her worldly experience. Preferring bathing suits with sleeves does not prevent her from hearing about skinny-dipping.