In the old Celtic tradition of SamHain or "All Saints Eve" it was believed that for the one night (October 31st) that signified the end of Autumn and the beginning of Winter, the dead could return to the land of the living to celebrate with their family, tribe or clan.
Extra places were set at the table and food set out for those who chose to return. This was known as a "Dumb Supper" where nobody spoke at the table while they awaited the return of their loved ones who had crossed over to the other side. Many believe this tradition was where the term "Dumb Supper" originated, but there are variations of the ritual in different cultures the world over.
Growing up in rural West Virginia my grandmother came to understand a slightly different version of the dumb supper that was passed from one generation to the next. This version of the ritual does not require it to be Halloween to practice it, although the desired outcome is similar.
If you wished to contact a recently deceased loved one you would set a dumb supper with extra settings for those who you wished to contact. You would then set the table in reverse order that you normally would, forks would be on the right side, etc.....All placements would be handled by two people while the table was being set, even the silverware.........You would then serve the food in reverse order as well beginning with dessert and ending with either soup or appetizers. This variation was also referred to as a "Backward Supper".
At some point during the serving of the first course and the last course of the meal, Your recently departed loved one would make contact. The contact could be verbal, it could be through noise association (two knocks for yes one for no) and in rare cases even visual manifestation.
From what my Grandmother remembers the reason for attempting to reach the loved one who had recently died was if there had been signs or "feelings" of restlessness that they may be confused and had not crossed over to the other side, perhaps due to circumstances surrounding their demise. The contact through the "Dumb Supper" was a way of helping them to cross over and finally find peace.