Q. Two very dear friends of mine have presented me with a social and emotional dilemma. I met this couple about a year ago and we immediately became close friends. Almost all of our social exchanges have been between me (a happy single) and them as a couple--that is, I spend time with A and B rather than with A or B. Well, this happy scenario has changed, because A and B have chosen to add a third person to their partnership. So now I am trying to decide what sort of adjustments I will make to accommodate this new C factor.

My dilemma is what to do in relation to C. I mean, I don't even know this person, and I'm not certain how much time I want to spend with C. Am I now obligated to invite all three of them if I want A and B to come to dinner?

I am not the sort who takes an instant liking to someone just because a friend thinks that person is likeable. Do you have any suggestions as to how I might go about maintaining a good relationship with A and B while getting acquainted with C?

A. This is an extremely interesting question to Miss Manners, as she feels it goes beyond your problem with A, B and C, to the fundamental issue, as it were, of what constitutes a social unit.

For example, we are just emerging from an unfortunate period in which the acceptable social unit was always two. At that time, your pleasant friendship with A and B would have been spoiled by their feeling that they could not invite you without some possibly dreary D, whose function would be solely to complete your unit; or you would have seen only A or B--whichever is of your gender--when the other was otherwise occupied.

Now we have more flexibility, but that naturally leads to confusion and the possibility of the unintended insult. Here is Miss Manners' current assessment of the social unit:

Weekdays, during the day, the social unit is the individual. You may ask anyone to lunch without having to ask anyone else. Nights and weekends, married and engaged couples must be invited as a unit, although they can accept--and should be accepted--as individuals. Unmarried couples of some duration may declare themselves a social unit, announcing that they prefer to go about socially together. Relative stability, rather than conventionality, is the requirement here. Two people of the same sex may declare themselves a couple, but a leftover one-night stand with an unknown last name is not eligible for invitations.

Now to your question--can three people be a couple? Fortunately, Miss Manners, who will issue rules when she must but prefers reverting to tradition, has a precedent on this one. It was decreed by Miss Manners' grandmamma, one of whose sisters, the artistic one, had a long and happy family life with two gentlemen. Like you, Miss Manners' grandmamma was not interested in the private aspect of this arrangment, but was sorely taxed--outraged, actually--by the havoc it wreaked on her dinner party seating arrangements.

She ruled that a social unit of three is permissible for large gatherings, but at a dinner party of 12 or fewer people, one cannot accommodate any one social unit consisting of more than two people. Which two, she didn't care; Miss Manners' great aunt could settle it at home, but was forbidden to bring more than one husband to intimate parties. Miss Manners sees no need to revise such a just settlement.