Introductions should be continued in the 21st century this is why as a host or whatever you are .You have to introduce yourself to everyone and introduce the guest of honor be it a birthday or funeral. This rule or practice has to go on in the 21st century because if not birthdays or whatever the event is about will not feel important. Now onto the second practice
R.S.V.P. respond if you please it comes from the french that's about all I know about its origins but it has to be passed down into this passing century.for when you or someone else has to plan seating or space availability for the people that may or may