Emily Post, whose books on manners have long been setting the etiquette standard, once lamented about the "flagrant disregard of old-fashioned convention" for sending and replying to formal invitations. That was back in 1922. What might she think today? Though fewer and fewer occasions require a formal response to an invitation, there are still times when you need to make sure you don't violate proper etiquette when accepting a formal invitation. Follow these instructions to the letter when you want to make sure your formal response is proper.
Get out your white or ecru letter paper and choose a pen with blue or black ink. Formal etiquette dictates that you write your response to an invitation by hand on your own personal stationery, which may or may not have a monogram.
Write in the third person. Put you and your spouse's name first, state you are accepting "the kind invitation of" the sender, and repeat the details about the day and time as a way for the hosts to confirm you have these details correct. Notice that formal responses include the guests' titles and social names but only the titles and surnames of the hosts. For example: Mr. and Mrs. Harold Dunn accept with pleasure the kind invitation of Dr. and Mrs. Smith to dinner on Friday the fifteenth of March at half past six o'clock
Center each line and follow the line breaks as shown.
Write the address on the envelope with the hosts' titles and full social names (for example, Dr. and Mrs. Edward Smith).
Send your response before the stated deadline. If no "reply by" date is mentioned, respond three days after receiving the invitation.
Don't feel locked into these formal rules. Use your best judgment and think about who is receiving the response. You don't want to write such a formal response that it makes you look pretentious. Never ignore a formal invitation, whether or not you plan to attend.