From the setting of the table until it is cleared for dessert, a plate must remain at every cover.

Under the first two courses there are always two plates.

The plate on which oysters or hors d’oeuvres are served is put on top of the place plate. At the end of the course the used plate is removed, leaving the place plate.

The soup plate is also put on top of this same plate. But when the soup plate is removed, the underneath plate is removed with it, and a hot plate immediately exchanged for the two taken away.

The place plate merely becomes a hot fish plate, but it is there just the same.

Emily Post