_That man may last, but never lives,
Who much receives, but nothing gives._
--Gibbons.
1) If you receive a written invitation, send a written reply. Let the
reply accord with the invitation in being either formal, or informal.
2) You will be thought discourteous if you fold your note carelessly,
write on soiled or ragged paper, use pencil instead of ink, or delay
your reply.
3) Accepting an invitation binds you, in honor, to carry out your
engagement. If circumstances prevent, at once inform the one who invited
you; and do it in a considerate manner.