Last Wednesday night, Emma emailed a dozen of our friends, inviting them to join us for Thanksgiving dinner. One reply arrived the next morning. Then nothing.

By Sunday evening, I had grown exasperated enough to send out a snarky followup:

The courtesy of a belated reply would be appreciated. So far, we've got exactly one RSVP.

It served its purpose. Replies cascaded in. Most, alas, said "no"; they had other plans.

Would that this were an isolated incident. Time and again, I've issued invitations that were not responded to. A simple "yes" or "no" is ideal. A "maybe" is acceptable too, especially if you follow up with a "yes" or a "no".

RSVP is not a meaningless formality. It's a vital planning aid. I need to know ahead of time whether to expect three or thirteen for a dinner party. It's rude and thoughtless to leave me hanging in limbo. If I assume that everyone who's been invited will show up, and cater accordingly, and many of them don't come, I've gone to needless expense and effort. If I guess that only half those invited will turn up, and I underestimate, then I'm embarrassed by not being able to feed my guests properly.

It's almost as big a sin for you to say "yes", then fail to show, without a word of warning.

When the stakes are low, such as a large drinks party, the lack of RSVPs is a minor matter. For a major production, it's inconsiderate at best.