What is with people not bothering to RSVP to party invitations? I mailed a couple of dozen pool party invites, and have had only three responses. I asked a couple of people in person if they are coming, and they said (1) “Probably not,” and told me about other things they were thinking of doing the day of my party, and (2) “Oh, didn’t my wife get back to you yet [to decline]?” My party is in one week, and I have no idea how many people to plan for, or even if I will have a party. Now I’m thinking of canceling, because it’s not the party I hoped for if only six people show up! It seems to be good etiquette that if you receive a written invitation—that includes a request for RSVP with phone and email—that people respond! Either I am extremely unpopular or people don’t have manners. What do you think? —Pool Party Postponed

Dear Party Postponed,

The last invitation I ignored was a gathering for drinks at a bar sent via the online party-planning site Evite. Since about 15 others were invited and I didn’t know the host well, I felt he wouldn’t care much if I were there or not. (And he was just inviting me to a bar, so it wasn’t like he had to know how much beer to get.) A few months passed, and I emailed him to ask if he could spare a few minutes for an interview. I wanted to ask him how he felt about my failure to RSVP. He shot back a terse email: He couldn’t do it. The lesson learned: If you don’t respond to an invitation, know that the host will notice and remember.

Now that we send most of our invitations via email, it’s all too easy to let an invite sink to the bottom of an overcrowded in-box. And when the host uses Evite or a similar service, guests can be particularly apathetic about responding. Some put off answering because they know they’ll get a reminder, at which point they can decide if they really want to come or not. Heather Allen, a graduate student at the University of Chicago, suggests another reason for delay. “Unless I know the hosts well, I don’t like to be the first person to respond. You don’t want to seem overly anxious or like you have nothing else to do.”

Even when an invitation is sent via old-fashioned snail mail, guests can be lax about replying. Getting a stamp and going to the postbox can seem an inconvenience. Etiquette-wise, it’s OK to respond to a mailed invite via email. But as a paper invite has no Reply button, it’s sometimes easy to forget to do so.

But here’s the thing: Hosts need to know who is coming so they can plan the food and drink, invite replacements if necessary, or even reschedule the event. Each time you don’t RSVP, you fall further in the host’s estimation. Eventually, if not immediately, you fall off people’s guest lists.

So you should answer an invitation as soon as you know if you’ll be able to make it, whether it’s a hand-painted card or a mass email. What if you’re unsure if you’ll have a business trip or an out-of-town guest? Marilyn Paul, author of It’s Hard to Make a Difference When You Can’t Find Your Keys: The Seven-Step Path to Becoming Truly Organized, advises: “Decide when you will know and mark that date on your calendar with a reminder to RSVP.” Then tell the host: “I’m delighted to receive your invitation. Given my other obligations, I’m unable to commit right now. May I let you know by such-and-such a date?” The host knows you got the invite, and why you haven’t replied yet. That way, he or she won’t worry that the reason you don’t want to commit is that you’re waiting for something better to come along.

Table Manners appears every Wednesday. Have a Table Manners question? Email Helena.