It seems so callous of children to grow up and leave the family home without family problems. For those parents who fail to amuse themselves with such modern devices as mid-life crises, law school or breaking up quarter-of-a-century marriages, we have therefore invented a new problem. It is called the "empty nest."

Miss Manners is not without tremendous sympathy for those so afflicted. She is resolutely in favor of adding generations onto families, rather than spinning off individuals -- provided, of course, that this takes place in enormous houses with porches, and that she is the eldest and gets to boss everyone else around. But as young people seem to be onto this scheme, and as most of the suitable houses have been made into condominiums, there are quite a few empty nests in the forest.

Much of the literature on the subject takes the optimistic approach of focusing on the gains -- bathrooms, closet space, the chance to get a word in edgewise at mealtime and so on. The tone is that of articles addressed to young working girls, assuring them that a dateless Saturday night is a fortunate opportunity for self-improvement. Miss Manners rather doubts that any of this fools anyone. To those used to heading a complicated household, the prospect of a simpler one, however filled with opportunity, is going to be disconcerting.

Miss Manners cannot exactly tell your adult children to stay home. She can, however, and will, tell everyone how to behave in regard to that home after they go. Is that a comfort?

It is certainly emotionally consoling, to both parent and child, to consider that the parental household is, in many ways, a home permanently available to those who have been nurtured in it. "This will always be your home; it is here whenever you need or want to come here" is the traditional speech, so grating to whatever family the child has acquired on his own.

The exceptions occur first to the people who still use the place as a house, not to the departed ones, who can afford to be more sentimental. No child can really understand and forgive the selfishness that prompts his parents to dismantle a shrine to his high-school years, to be visited by the former owner faithfully at least once a year, simply to turn it into a study or guest room for their own convenience. For those who can stand having football pennants or pictures of rock stars torn from magazines on their upstairs sitting room wall, compromise is sometimes possible.

However, the children don't care to decorate their sophisticated new homes that way, and must therefore swallow their indignation if their old rooms are cleaned out. The parental offer of hospitality is not considered violated unless there is no place at all for a returning child to stay.

There need not be a place for yearbooks, old volleyballs and dried prom flowers. If there is family attic space available, the parents can try to live up to the child's expectations of devotion by pretending to be unable to part with any of his primary school arithmetic workbooks, but many perfectly adoring parents are content with one graduation photograph and one crayoned drawing per grown-up child. "Come and get all this junk if you want it, otherwise I'm throwing it out" is a perfectly proper remark for a loving parent to make to a child who lives elsewhere. Time limits are even advisable.

Whatever the adjustment in quarters, it will serve to make the point that the child is, if not a guest in his parents' house, not a resident, either. The more guestlike courtesies the child performs, the greater his welcome.

Having told children since they were small that no, they are not equal to their parents and not entitled to say, "If you do it, why can't I?," Miss Manners finds it difficult to get them into the habit of treating their parents as they would wish to be treated. A grown-up child who would be outraged to have his parents descend upon him without notice, refusing him the dignity of privacy or control over his own schedule, nevertheless fails to consider that his parents might occasionally make plans that would be disrupted by unannounced visits.

Only when one scrupulously asks if it would be convenient to drop in, for an hour to pore through the attic, a week to save money between apartments, or a month to recover from a bad romance, is one told, "Darling, you don't have to ask. This is your home, and it always will be. Come whenever you want; the door is always open."

Miss Manners highly approves of this statement -- but not of those who take it literally. Q.Q. I attended a women's awards luncheon recently, at which we were served a lettuce wedge. This was my first exposure to this type of salad, and unless you can give me some advice, I hope it will be my last. Q.

A quarter of a lettuce head is obviously easy for the kitchen to prepare, but it's hell to eat. No one seemed to know whether to tackle it by cutting from the ends, the middle or where. Once covered with dressing, the wedge slips and slides on the plate, splattering you and the tablecloth, and making itself difficult to cut into bite-sized pieces.

Everyone in the room was struggling with the same problem, while trying to appear reserved and dainty, as we were all dressed up. Some handled the situation by just not eating the salad, but I was hungry! Is there a proper and not extremely difficult way to eat a lettuce wedge? A.A. No. The proper way, cutting it with the edge of the fork, is difficult, if not impossible; and the easy way, tearing it leaf from leaf with your fists, is improper. A.

Technically, your hosts could have given you salad knives, but Miss Manners knows they didn't. Anyone who would serve lettuce wedges to ladies in silk blouses would not be that considerate.

The choice is: starve or use the meat knife. Not approving of either of these solutions, Miss Manners will look the other way. Q.Q. How does one teach an adult to say "thank you" and to give compliments, as well as accept them?Q.

My boyfriend is no child, but is severely lacking in these matters of common courtesy. I am unsure whether this is due to genetic imbalance or lack of proper training as a boy.

Sometimes, he will respond correctly when he hears me thank a hostess, but at other times he acts like my thank you is sufficient for both of us. It is not.

He has offended my mother by never thanking her for inviting him to dinner, and has offended me as well. I am not bragging, but I have done many nice things for him with nary a "thank you." The simplest task would be greatly rewarded if he would only verbally acknowledge it.

As if this breach weren't annoying enough, he is also terrible about complimenting others. Recently we dressed up for a nice dinner out with his mother. I complimented him; he never returned the favor.

Am I overly sensitive, or am I right in suspecting that he is bascially rude and self-centered? Is there any hope for him? A.A. It is rude to attempt to improve the behavior of anyone other than one's own minor children, unless you have been sincerely asked to do so. Even Miss Manners only enlightens upon request.A.

But although most people nowadays would agree with this principle in regard to the teaching of manners -- at least to the very idea of anyone else's teaching them manners -- they no longer recognize that it should extend to other areas, such as health, attitude and manner of expression. Miss Manners believes it does, but she recognizes the opportunity for you to take advantage of the general opinion.

Thus you may be able to teach this gentleman manners, provided you not label them as such, but disguise them with encounter-therapy jargon:

"I'm sure you don't realize it, but the people we visit often think I'm just dragging you along and you really hate to come." He looks surprised and asks why anyone would imagine any such thing. "Well, you know, they've all been brought up to say 'thank you' automatically to hostesses, and so they think that you must have a deep reason for not doing so. My mother, for instance, is convinced you don't like her."

"Do you resent my doing things for you? Oh, yes, you must. I know you don't want to hurt my feelings, but I can't help noticing that you never say anything when I try to please you, so I must be doing it all wrong."

"I wish I knew what you like to see me wear. I know it's foolish, but I would like so much to please you, and sometimes when I've taken a lot of care to get dressed up and then you never say anything, I feel so deflated. I suppose you don't like it and avoid saying anything so you won't hurt my feelings."

Personally, Miss Manners is made sick by this style of talking, but then, she does her reforming on a grand scale. Nevertheless, she admires you for undertaking to save a single soul and hopes this technique will be of use. It should at least tell you whether he is self-centered, in addition to being rude.