It strikes Miss Manners that a sure-fire way to get perfect housemates would be:

- Approach them when they are helpless and impressionable.- Administer detailed daily lessons in whatever you consider to be the right way to live.

- Supervise them for years to make sure they get it right.

So why do parents complain that their household peace is shattered when their adult children continue or return to live at home?

Miss Manners figures that some parental groans about having their children at home are purely conventional. Too modest to brag that people who know them only too well actually want to live with them, they claim that the attraction must be free or cheap board and services.

Others may be saying this to protect their children from worse outside attacks. Few people hesitate, when they hear of such a situation, to express the modern assumption that adults who live with their parents are financial, romantic and psychological failures - unable to get decent jobs, stingy, emotionally stunted, lazy, irresponsible, bad marriage prospects, self-indulgent and afraid to face the world.

Welcome home, kids.

Why society should consider it healthy and normal for parents and children to want little to do with one another once they are free to seek more agreeable company, Miss Manners does not know. But this is so ingrained that both parents and children will automatically dispense with any semblance of family loyalty to volunteer that the arrangement is only an emergency measure of last resort.

Thanks, folks.

The result is an unseemly display of family disloyalty, based on the notion that affection between parents and children is, at best, a temporary state from which they can all hardly wait to be released.

Perhaps it is that bad, although Miss Manners does not consider this justification for advertising family antipathy. But as these people have already lived together satisfactorily enough to make them all willing to try again, what went wrong?

Everyone involved agrees that the difficulty lies in an inability to adjust properly from the behavior appropriate to parents and minor children now that the children are major. They just differ as to whether a change should involve increased freedom for the children while the responsibilities remain the same for the parents, or increased responsibility for the children while the parents' restrictions on their freedom remain the same.

And they use the wrong paradigms. An adult child living at home is neither a guest, who is waited upon, nor a tenant, who is charged rent. The parent is neither a host, who must put up with whatever behavior the guest chooses to inflict, nor a landlord, with no intrusive interest in the tenant's health and happiness.

Rather, the grown-up child is a full member of the household, which means not creating burdens for others and pitching in with work and money that is needed. (Just as Miss Manners has never believed in paying one's own small children for doing chores, she doesn't believe in charging them for accommodations; the home is not a marketplace.)

Adult children are likely to have ideas, tastes and habits that differ from their parents, but such is also true of husbands and wives, the many near-equivalents of such that we seem to have among us, and of less-exciting arrangements for shared housing.

Adults who live together are expected to work out compromises that don't unduly annoy, worry or outrage one another - not only in questions of noise, food and cleanliness, but by declaring more or less when they expect to be home, obtaining agreement for house guests, and borrowing one another's belongings only with permission.

If they are able to do this, they may find that they are together for the most bizarre of reasons: because they enjoy one another.