Summary

Portrait of Lillian Eichler Lillian Eichler Book of Etiquette, Volume 1, Part 2… (1921)

No matter how informal, an invitation should always be acknowledged within a week of its receipt. It should be a definite acknowledgment—either an acceptance or refusal—and no doubt should be left as to whether the writer intends to be present or not. An invitation must always be answered in kind; that is, a formal invitation requires a formal reply, following closely the wording of the invitation. The informal invitation should be cordial enough to warrant a cordial and friendly reply; both invitation and acknowledgment should be free of all stilted phrasing.
Source: Wikisource

Portrait of Lillian Eichler Lillian Eichler Book of Etiquette, Volume 1, Part 2… (1921)

The host or hostess planning a theater or opera party should strive to have an equal number of men and women guests. For this reason, the person who receives an invitation should make prompt reply, so that if he or she is unable to attend, someone else can be asked to take the place. It is not necessary to have invitations engraved for these occasions; in fact, a brief note, written with just the correct degree of formality, yet with no sacrifice of cordiality, is much to be preferred.
Source: Wikisource

Portrait of Lillian Eichler Lillian Eichler Book of Etiquette, Volume 1, Part 2… (1921)

When a vacancy occurs in a dinner party at the last moment, one may call upon a friend to fill the place as a special courtesy. This is an instance when tact and discretion are important, for not everyone is broad-minded and sensible, and some people may take offense at being asked to take the place that someone else relinquished. A short cordial note should be written, explaining the situation, and frankly asking the friend to come in the place of the invited guest who cannot be present.
Source: Wikisource

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