Recently, we invited a family for dinner and of course had the meal planned, including homemade ice cream. My kids were really looking forward to it, since the homemade ice cream is a rare treat. When the invitation was originally accepted, the wife asked if she could bring anything, and I said, “Just an appetite!”

When they showed up, they brought a carton of store-bought ice cream and said they thought they’d “bring” dessert, and the husband said that this brand was his favorite. After a split second of panic, I just decided to serve their ice cream while trying to figure out what to do with all the ingredients I had purchased for the homemade kind. To my knowledge, they never knew they screwed up our dessert plans.

I thought I handled it OK, but I have two questions: Is there a better way to handle the situation if it, unfortunately, happens again? And, do you consider it rude to bring a course to a meal, expecting it to be eaten, when the guest did not inform the host ahead of time? —Homemade Is Best

Dear Homemade Is Best,

Bringing an extra dish to someone else’s dinner is like bringing an extra person: Your guest should always ask first. You’ve put careful thought into the menu and the social mix, and a surprise addition could clash with either one. Plus, it can feel a little insulting, as if the guest is worried that what you’ve provided won’t be sufficient.

But in some parts of the United States, showing up empty-handed is the faux pas. Danielle Searls, a painter who now lives in San Francisco, says when she was growing up in Minnesota, it was customary to bring a dish to someone else’s dinner, often a hotdish (a kind of casserole). “My specialty was Tater Tot hotdish,” reminisces Searls. In many areas, this tradition persists. “It’s always assumed it’s a potluck,” she says.

If people are hard-wired to bring a dish, it can be pretty hard to stop them. Saying “No need to bring anything except yourselves” won’t help. They’ll just brush it off as a polite platitude. Instead, suggest a different way for them to satisfy their need to give. Ask them to bring wine or do you a non-food-related favor like lend their folding chairs.

If guests bring a dish, you must serve it, even if your menu is an homage to the cuisine of Alsace-Lorraine and they’ve brought a Carvel ice cream cake. Your guests have gone to the trouble of buying or making a dish. It would be disrespectful to thrust their offering to the back of the fridge.

Though they shouldn’t bring a casserole or a pint of Ben & Jerry’s, guests should bring something. When you cook a meal for others, even if it’s just an omelet, you’re giving them a wonderful gift, and they should offer a token of appreciation. Wine, flowers, and chocolates are the classic choices for host gifts. You need not bring anything expensive. One of the nicest hostess gifts I received was a collection of interesting spices: star anise, dried orange peel, and garam masala. Or consider bringing a book. If the book is special to you, it doesn’t matter if it’s secondhand.

Some spiritually enlightened hosts claim that their guests’ presence is gift enough. But gift-giving benefits the giver too. If this sounds schmaltzy, know that there’s neurological evidence. In one study, volunteers played a computer game in which they had to make a series of financial decisions, including choosing between donating to charity and taking a payoff. Functional MRI scans showed that both acts were associated with increased activity in the midbrain—the area that corresponds to satisfying primal desires, like those for food and sex. So giving a gift offers the same kind of pleasure as eating a nice meal.

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